Labflow Prelab Quizzes 7-12
Suppose you have 150.0 mL of a 0.250 M sodium hydroxide solution. How many moles of sodium hydroxide are in the solution?
0.0375 The definition of molarity is Molarity=moles of solute/liters of solution
How many moles of HClHCl are in 47.3 mL47.3 mL of a 1.65 M HCl1.65 M HCl solution?
0.078 Molarity, M, is moles of solute, moles, per liters of solution, V. M=moles/V
Sugar is easily soluble in water and has a molar mass of 342.30 g/mol. What is the molar concentration of a 249.8 mL aqueous solution prepared with 72.9 g of sugar?
0.853 The definition of molarity is Molarity=moles of solute/liters of solution
Determine the type of alcohol corresponding to each given description or name.
1-pentanol- Primary alcohol 3-ethyl-3-pentanol- Tertiary alcohol 2-hexanol- Secondary alcohol An alcohol with two other carbons attached to the carbon with the hydroxyl group-Secondary alcohol An alcohol with one other carbon attached to the carbon with the hydroxyl group-Primary alcohol An alcohol with three other carbons attached to the carbon with the hydroxyl group-Tertiary alcohol A primary alcohol has one other carbon attached to the carbon with the hydroxyl group. Because the name 1-pentanol indicates that the hydroxyl group is on the terminal carbon in the molecule, it is an example of a primary alcohol. A secondary alcohol has two other carbons attached to the carbon with the hydroxyl group. Because the name 2-hexanol indicates that the hydroxyl group is on a carbon within the chain, it is an example of a secondary alcohol. A tertiary alcohol has three other carbons attached to the carbon with the hydroxyl group. Because the name 3-ethyl-3-pentanol indicates that the hydroxyl group is on a carbon within the chain that has another carbon chain substituent (ethyl), it is an example of a tertiary alcohol.
Calculate the percent by mass of a solution made from 14 g NaCl (the solute) and 67 g water.
17 The definition of percent by mass for a solution is % mass of a solution=mass of solute/mass of solution×100
Suppose you need to prepare 126.7 mL of a 0.270 M aqueous solution of NaCl. What mass, in grams, of NaCl do you need to use to make the solution?
2 The definition of molarity is Molarity=moles of solute/liters of solution
The addition of chromic acid or chromate is a qualitative test for alcohols as the reaction causes a color change. However, not all alcohols react with chromic acid or chromate.
3-hexanol-Color change 1-butanol-Color change 3-ethyl-3-pentanol-No color change 2-pentanol-Color change Chromic acid acts as an oxidant and requires a hydrogen on the carbon to be oxidized. Therefore, only primary and secondary alcohols react with the oxidant and trigger the color change. Tertiary alcohols, like 3-ethyl-3-pentanol, do not have a hydrogen on the carbon of the alcohol group and do not trigger the color change.
What is the correct reading of the volume in the pictured buret? Make sure to report your reading with the appropriate significant figures.
39.95 mL Determine the volume in the buret based on the bottom of the meniscus. Note that volume markings increase going down the buret. Therefore, with the meniscus above the 40 mL line, the correct volume is less than 40 mL. The bottom of the meniscus falls right in the middle of the space between the tick mark for 39.9 mL and 40.0 mL. Therefore, a good estimate of the volume is 39.95 mL. You should always report the reading with one estimated digit past the smallest marking by noticing where the bottom of the meniscus falls between the tick marks.
Suppose you separate a 2.65 g mixture of sand and salt and recover 1.20 g of salt. What is the percent by mass of salt in the mixture?
45.3 The equation for the percent by mass of a mixture component is % composition=(mass of mixture component/total mass of mixture)×100
A hydrocarbon is saturated if only single bonds are present. Alkanes are saturated hydrocarbons. A hydrocarbon is unsaturated if any multiple bonds are present. Alkenes are unsaturated hydrocarbons.
A hydrocarbon is saturated if it has only single bonds present because each carbon has as many hydrogens around it as possible. Alkanes only have single bonds and are saturated hydrocarbons. A hydrocarbon is unsaturated if any multiple bonds, like double or triple bonds, are present. Therefore, alkenes and alkynes are unsaturated hydrocarbons.
Baeyer's test, also known as the permanganate test, shows the presence of alkenes. A positive Baeyer's test appears as a brown precipitate. A negative Baeyer's test appears as a purple solution.
Baeyer's test indicates the presence of alkenes and alkynes through their formation of manganese(IV) oxide when reacting with potassium permanganate in solution. If an alkene or alkyne is present, the brown precipitate of manganese(IV) oxide forms. If no alkenes or alkynes are present, the solution remains the purple color of the potassium permanganate.
Benedict's test shows the presence of reducing sugars. A positive Benedict's test appears as a reddish precipitate. A negative Benedict's test appears as a blue solution.
Benedict's test indicates the presence of reducing sugars through their reaction with copper ions in solution. If a reducing sugar is present, a precipitate with a color somewhere between yellowish-green and red forms, depending on the concentration of the reducing sugar. If no reducing sugars are present, the solution remains the blue color of the copper ions.
Consider the reaction of bromine with the pictured alkene.
Bromine reacts with alkenes by adding across the double bond. Therefore, a bromine is added to each carbon that had participated in the double bond and the double bond is a single bond.
When using acids and bases, note that these substances are _____________. Make every effort to avoid contact with __________________. Be sure to wipe up any spills ___________.
corrosive; the skin and lab surfaces; immediately
Fructose is an example of a ketohexose. The -hexose part of the name indicates that fructose is a monosaccharide that contains 6 carbons. The keto- part of the name indicates that fructose contains a ketone functional group. Fructose can combine with glucose to form sucrose. Therefore, sucrose is a disaccharide.
A ketohexose is a 6-carbon monosaccharide that contains a ketone functional group. The keto- part of the name indicates that a ketone appears in the chain form of fructose. Because only one unit of a sugar is present, it is a monosaccharide. The -hex- part of the name corresponds to the numbering prefix indicating 6, which is the number of carbons when discussing carbohydrates. If two monosaccharides combine with a glycosidic linkage, a disaccharide is formed. Adding more monosaccharide units creates a polysaccharide, which is a complex carbohydrate.
Identify the type of sugar corresponding to each name. Fructose-Monosaccharide Sucrose-Disaccharide Lactose-Disaccharide Glucose-Monosaccharide Starch-Polysaccharide
A monosaccharide is the simplest form of a carbohydrate. Glucose and fructose are two of the most common monosaccharides. Disaccharides and polysaccharides are respectively two or more monosaccharides bonded together. Sucrose and lactose are common disaccharides. Starch is a polysaccharide, which involves a large number of glucose monosaccharide units.
Consider the pictured structure of a dipeptide. What does each label on the structure represent?
A: N-terminus B: peptide bond C: chiral center D: C-terminus The dipeptide is two amino acids bonded together by a peptide bond. The peptide bond is the amide in the middle of the structure. The ends of the molecule are the N-terminus, where the nitrogen is, and the C-terminus, where the carbon of the carboxylate is. There is one chiral center in this structure as there is only one tetrahedral carbon with four different substituents. Most amino acids have a chiral center at this position.
Which tests show can be used to show that a phenol is present?
Acidity test Iron(III) chloride test Both the acidity test and the iron(III) chloride test show the presence of phenols. The acidity test reacts a base with phenols to deprotonate them and easily dissolve them. In the iron(III) chloride test, a phenol becomes a ligand on iron and changes its color. The Lucas test reacts with secondary and tertiary alcohols. The iodine test shows the presence of starch and should not be confused with the iodoform test.
In general, alcohols dissolve when mixed with water because the O-H bonds in alcohols can hydrogen bond with water.
Alcohols generally dissolve in water because the O-H bonds of the hydroxyl group can hydrogen bond with the O-H bonds in water. The interaction allows the molecules to intersperse and dissolve.
What is the best safety approach when working with unknown chemical substances?
Assume that the substance is hazardous. Always wear appropriate PPE and take steps to prevent contact.
When reacting yeast with sugars, what is the most prominent evidence that fermentation has occurred?
Formation of a gas Fermentation converts a sugar into ethanol and carbon dioxide. Carbon dioxide is a gas which will bubble out. Therefore, the visual proof of fermentation is the formation of a gas as bubbles in solution.
Determine whether each of the given characteristics refers to electrolytes or non-electrolytes.
Dissociate in solution- Electrolytes Do not dissociate in solution- Non-electrolytes Conduct electricity in solution- Electrolytes Do not conduct electricity in solution- Non-electrolytes Examples includeC6H12O6C6H12O6 and CCl4CCl4- Non-electrolytes Examples include NaOHNaOH and KBrKBr-Electrolytes Electrolytes are substances that dissociate in solution, forming ions. Solutions of electrolytes can conduct electricity. Examples of electrolytes include NaOHNaOHand KBrKBr. Strong electrolytes dissociate completely, while weak electrolytes only dissociate to a certain degree. Non-electrolytes are substances that do not dissociate in solution. Solutions of non-electrolytes do not conduct electricity. Examples of non-electrolytes include C6H12O6C6H12O6 and CCl4CCl4.
In order to use a pipet, place a bulb or pump at the top of the pipet. Use this object to fill the pipet such that the meniscus of the liquid is even with the volume line. Release the liquid, touching the tip of the pipet to the side of the container if necessary to release the last drop outside the pipet tip.
Follow the process as described to ensure accuracy when using a pipet. The volume specified on the pipet is accurate only if the correct steps are used.
Determine whether each statement describes a solution of a strong electrolyte, weak electrolyte, or non-electrolyte.
Has the highest conductivity-Strong electrolyte solution Has little or no conductivity-Nonelectrolyte solution Contains a completely dissociated solute-Strong electrolyte solution Contains a partially dissociated solute-Weak electrolyte solution Has a medium level of conductivity-Weak electrolyte solution Contains a complete solute-Nonelectrolyte solution Strong electrolytes are highly soluble ionic compounds that completely dissociate in solution. Thus, strong electrolytes have the highest conductivity in solution. Weak electrolytes are partially soluble ionic compounds that partially dissociate in solution. Thus, weak electrolytes can conduct electricity in solution but not as well as strong electrolytes. Nonelectrolytes are compounds that do not dissociate in solution, such as molecules. Thus, nonelectrolytes are not good at conducting electricity
How can you remove the protein casein from a sample of non-fat milk?
How can you remove the protein casein from a sample of non-fat milk? Casein can be removed from non-fat milk by adding acid. The pH change interrupts the tertiary structure by changing the charges in the protein. The protein then solidifies as a precipitate which allows its removal by filtration. If fat were present in the milk, it would interfere with this process.
In general, when hydrocarbons like oil are added to water, the two liquids do not mix because hydrocarbons are non-polar and water is polar.
Hydrocarbons and water generally do not mix. The hydrocarbons are not soluble in water because they are non-polar and water is polar.
In general, when a hydrocarbon is added to water, the hydrocarbon will float above the water because hydrocarbons are less dense than water.
Hydrocarbons are generally less dense than water so they float on top, like the example of oil on water.
The biggest concern of working with hydrocarbons in lab is that many of them are flammable. Therefore, hydrocarbons should be handled in the hood to contain any associated vapors with that hazard.
Hydrocarbons are made from carbons and hydrogen and can be gases, liquids, or solids. The hazard that many of them have in common is flammability. Even the liquids or solids often give off vapors that are flammable. Because so many hydrocarbons have hazardous associated vapors, they should be handled in the fume hood.
Identify the type of hydrocarbon represented by each structure.
Hydrocarbons are usually classified by the highest order of bond present. Alkanes only have single bonds, whether in a linear or cyclic formation. Alkanes in a ring formation are often called cycloalkanes. Alkenes have at least one double bond. Cyclic alkene structures can specifically be called cycloalkenes. Alkynes have at least one triple bond. Cyclic alkynes generally do not exist because of the linear arrangement around the bond. Aromatic compounds have specific requirements. An aromatic hydrocarbon has carbons in a ring and alternating single and double bonds, which create stability through the delocalization of the electrons. The most common aromatic ring size is six carbons but others do exist.
Identify the expected result of the iodine test with different carbohydrates. Amylose-Blue-black solution Sucrose-No reaction Cellulose-Red-brown solution Glycogen-Red-purple solution
Iodine reacts with polysaccharides. Thus, iodine does not react with the disaccharide sucrose. When iodine reacts, the solution color depends on the structure of the polysaccharide. The helical shape of amylose in starch traps iodine to form a blue-black color, which is the most prominent use and result of the iodine test. However, iodine can also react with other polysaccharides, like cellulose, forming a red-brown solution, and glycogen, forming a red-purple solution.
Jones's test, also known as the chromic acid test, shows the presence of primary or secondary alcohols. A positive Jones's test appears as a color change to green. A negative Jones's test appears as an orange solution.
Jones's test indicates the presence of primary or secondary alcohols by reducing the chromium(VI) in chromic acid to chromium(III). Secondary alcohols are oxidized to ketones. Primary alcohols are oxidized to carboxylic acid by first creating an aldehyde. For this reason, aldehydes also give a positive test. Tertiary alcohols do not react. If a primary or secondary alcohol or aldehyde is present, the characteristic blue-green color of chromium(III) appears. If only tertiary alcohols or no alcohols or aldehydes are present, the solution remains the orange color of the chromium(VI) in chromic acid.
A neutralization reaction is a reaction between ___________ that results in the formation of ___________ and ________________.
an acid and base; water; salt
Predict the products of hydrobromic acid, HBr, reacting with magnesium hydroxide, Mg(OH)2Mg(OH)2.
MgBr2 H2O Magnesium hydroxide is Mg(OH)2 and hydrobromic acid is HBr. Neutralization reactions are a type of double replacement reaction, where the ions switch partners.
Primary and secondary alcohols can be oxidized by the addition of an oxidant like chromic acid or chromate. What is the product of oxidizing 1-propanol with the shown structure?
Oxidation of an alcohol has the effect of removing a hydrogen from both the carbon and oxygen of the alcohol. A double bond carbonyl is then created, which represents the oxidation of the carbon. A primary alcohol, like the pictured 1-propanol, is oxidized to an aldehyde
Aspartame is the methyl ester of a dipeptide made of phenylalanine and aspartic acid. What are the expected products of the hydrolysis of aspartame?
Phenylalanine Aspartic acid Methanol Hydrolysis of aspartame breaks the peptide bond between the two amino acids and reacts with the methyl of the methyl ester. Therefore, the expected products are the two amino acids as well as methanol. The peptide bond will not remain intact so formamide is not a product. Alanine is a separate amino acid that does not appear in aspartame and will not be a product. Aspartame follows a different pathway when heated, rearranging to diketopiperazine.
Denaturing is the process of interrupting a protein's structure so that it no longer functions. Which level of structure is NOT affected by denaturing a protein? Multiple reagents or changes can denature a protein. Which listed change will NOT denature a protein?
Primary structure Adding water Denaturing interrupts the interactions between protein units or parts of proteins. Therefore, secondary, tertiary, and quaternary structure can all be affected by denaturing. Denaturing does not interrupt primary structure as the peptide bonds do not break. Any significant condition changes can denature a protein. However, adding water to a protein does not generally disrupt its function as proteins function in aqueous situations.
Identify whether each substance is an acid or base.
RbOH- base HNO2- acid Ba(OH)2- base KOH- base HClO4- acid BrØnsted-Lowry acids have one or more protons that can be donated, while bases are proton acceptors. An acidic proton, -H, in a chemical formula indicates that a substance is an acid. A hydroxide group, -OH, often indicates that a substance is a base. In an acid-base reaction, the hydrogen from an acid can combine with the hydroxide from a base to form water.
Determine whether or not each hydrocarbon is saturated.
Saturated compounds have as many hydrogens around each carbon as possible, which is achieved by only having single bonds present. Thus, the two structures that only have single bonds are saturated. The two structures with multiple bonds, a double bond and triple bond respectively, are unsaturated hydrocarbons.
Seliwanoff's test shows the presence of ketoses. A positive Seliwanoff's test appears as a red solution. A negative Seliwanoff's test appears as a light pink solution.
Seliwanoff's test indicates the presence of ketoses, which are carbohydrates with a ketone functional group. Therefore, any carbohydrate size can react if there is a ketone. If a ketose is present, the solution quickly becomes red, based on the fast reaction of a ketone with the resorcinol. If only aldose carbohydrates are present, the solution still reacts but much slower and only reaching a light pink color.
When sodium chloride, NaClNaCl, dissolves in water, the solution contains sodium ions and chloride ions in addition to the water solvent. The partial charges in water help dissolve the compound as the hydrogen end of water is attracted to the chloride ion and the oxygen end is attracted to the sodium ion.
Sodium chloride dissociates completely in water into sodium ions, Na+Na+, and chloride ions, Cl−Cl−. There is a strong attraction of the ions to the partial charges in water. Specifically, the Cl−Cl− ion is attracted to the slightly positive hydrogen end of water and the Na+Na+ ion is attracted to the slightly negative oxygen end of water.
When sucrose is hydrolyzed, two reducing groups will be created as the glycosidic linkage is broken. Hydrolyzed sucrose will give a positive Benedict's test. Hydrolysis can be achieved by adding strong acids or enzymes.
The addition of a strong acid or an enzyme can break the glycosidic linkage in a disaccharide like sucrose. The result of the breakage are two monosaccharides with hemiacetals that can act as reducing ends. The reducing groups will give a positive Benedict's or Fehling's test.
Biuret test shows the presence of a tripeptide or larger peptide. A positive Biuret test appears as a violet solution. A negative Biuret test appears as a blue solution.
The biuret test indicates the presence of proteins that have at least two peptide bonds, which is a tripeptide or larger. The peptide bonds can bond as ligands to the copper ions in the biuret reagent. If a protein is present, the solution becomes a violet color. If no large enough protein is present, the solution remains the blue color of the copper ions.
The bromine test shows the presence of alkynes. A positive bromine test appears as a colorless solution. A negative bromine test appears as an orange solution.
The bromine test indicates the presence of alkenes and alkynes through their reaction with bromine. If an alkene or alkyne is present, the solution becomes colorless as bromine is added across the double or triple bond. If no alkenes or alkynes are present, the solution remains the brownish orange color of bromine.
When working with chemicals that are corrosive, it is particularly important to minimize the risk of contact with the body, lab surfaces, or other materials. Proper personal protective equipment includes gloves and safety goggles.
The experiment Quantifying the Composition of Limestone requires certain chemicals that are corrosive. Be sure to review all safety precautions before starting the lab. Gloves and safety goggles are required, and try to avoid contact of these substances with the body, lab surfaces, or other materials.
The iodine test shows the presence of starch. A positive iodine test appears as a color change to blue-black. A negative iodine test appears as a yellowish solution.
The iodine test indicates the presence of starch through the formation of an iodine-starch complex, which has a characteristic blue-black color. If starch is present, the solution becomes blue-black. If no starch is present, the solution remains the yellowish color of the iodine solution.
Small 3D features determined by hydrogen bonding-Secondary structure Overall 3D shape of a protein-Tertiary structure Interaction of multiple of protein units-Quaternary structure The sequence of amino acids- Primary structure
The levels of structure increase by scale from primary to quaternary. The primary structure of a protein is the sequence of amino acids bonded to each other. The secondary structure of a protein is the local, small structures based on hydrogen bonding. Some common examples are the alpha helix and the beta pleated sheet. The tertiary structure of a protein is the overall 3D shape of a protein, which might be determined by ionic or hydrophilic interactions. Not all proteins have quaternary structure. Quaternary structure is the interaction of multiple separate protein units.
Eugenol is a molecule that contains the phenolic functional group. Which option properly identifies the phenol in eugenol?
The phenolic functional group is the benzene ring directly attached to the hydroxyl group, which makes it a type of alcohol. Therefore, both the benzene ring and the hydroxyl group need to be pointed out when identifying the phenol part of the molecule.
Fehling's and Benedict's tests are related qualitative tests for the presence of aldehydes based on their reaction with Cu2+Cu2+ ions in basic solution.
The reaction of aldehydes with Cu2+Cu2+ ions in basic solution results in a carboxylate ion and copper(I) oxide, Cu2OCu2O. The aldehyde is oxidized to the carboxylate. The basic solution keeps this product deprotonated, rather than forming the carboxylic acid. The copper ion is reduced to the copper(I) oxide, which precipitates and signals a positive test. Water is also a product in the reaction to balance the equation.
The ninhydrin test shows the presence of amino acids. A positive ninhydrin test appears as a color change to purple. A negative ninhydrin test appears as a colorless solution.
The reaction with ninhydrin indicates the presence of amines or amino acids through a Schiff base mechanism that produces a chromophore. If an amino acid is present, the solution turns pinkish purple. If no amines are present, the solution remains colorless.
In the titration setup in lab, the buret will be filled with base. During the titration, a beaker placed underneath will contain acid and indicator.
The titrant, or the substance in the buret, is the base. This will the strong base NaOH for two titrations and the weak base NH3 for one titration.
Determine the type of alcohol represented by each structure.
The type of alcohol is based on what is bonded to the same carbon as the hydroxyl group of the alcohol. The rest of the molecule does not impact the type of alcohol. A primary alcohol has only one other carbon attached to the carbon with the hydroxyl group. A secondary alcohol has two other carbon attached to the carbon with the hydroxyl group. A tertiary alcohol has three other carbons attached to the carbon with the hydroxyl group. In a phenol alcohol, the carbon with the hydroxyl group is part of a benzene ring.
Some carbohydrates are classified as reducing sugars due to their ability to reduce other reagents. What features of a carbohydrate usually indicate that it is a reducing sugar?
There is a hemiacetal in the ring form. There is an aldehyde in the chain form. A reducing sugar involves an aldehyde that can be oxidized. In the chain form, the aldehyde is immediately apparent. In the ring form of a sugar, a hemiacetal usually indicates a reducing sugar because it can be opened into an aldehyde. An acetal cannot be opened into an aldehyde. Some disaccharides can be reducing sugars but only if the proper functional groups are present.
Determine whether each of the properties described applies to volumetric or graduated glassware.
Used for applications in which great accuracy is needed-volumetric Designed to measure one specific volume of liquid-volumetric Capable of measuring a range of volumes of liquid-graduated Volumetric glassware is designed to accurately measure and dispense one specific volume of liquid, such as the volumetric pipette pictured here. Graduated glassware may be used to measure and dispense a range of volumes of liquid, but with less accuracy, such as the graduated pipette pictured here.
Which of the pictured molecules is the most polar molecule?
Which of the pictured molecules is the most polar molecule?
Match each description to the correct term.
a liquid that dissolves another substance-solvent a liquid consisting of one substance dissolved in another-solution a value used to describe the amount of one substance dissolved in another-concentration a chemical that is dissolved-solute A solution consists of a solute dissolved in a solvent. The amount of dissolved solute is described by the concentration of the solution.
