lab final
If the freezing point depression for a solution is 2.5°C and Kf = 4.5°C/m, what is the molality of the solution?
.56 m - To calculate the molality, divide the temperature by Kf. The molality is 0.56 m.
be able to recognize
double displacement rxns, combustion, single replacement, decomposition rxns
When the required amount of one solution has been added to the second solution to complete the reaction
equivalence point
Which transition would correspond to the highest frequency of light emitted?
n = 4 to n = 1
The reaction between sodium hydroxide and hydrochloric acid is considered which type?
neutralization
not empirical formulas
not empirical b/c they can be reduced C6H12O6 K2C2O4
physical change examples:
- A liquid freezes into a solid. - A solid dissolves into water. -
which are empirical formulas
Ba3(PO4)2 NaMnO4 CaCO3
Which compounds could be represented by the empirical formula CH2
C8H12 C2H4 C3H6
flask
Containing a stirred reaction mixture
For each described liquid, determine the behavior of a hydrometer calibrated around the density of pure water. In a liquid that is more dense than water...
Float higher than position in pure water
In the reaction of magnesium metal with hydrochloric acid, how do you determine when the magnesium metal has reacted completely?
Gas bubbles are no longer produced. and The magnesium metal is gone.
graduated cylinder used for
Measuring out a volume of liquid
(l) in a chem rxn means
The substance is a liquid.
Which has a greater energy, long wavelength red light or short wavelength UV light?
UV light
Glassware that allows a solution to be precisely and slowly added to another solution
burette
Solution of known concentration that is slowly added to a solution of unknown concentration
titrant
chemical change examples
- A precipitate is formed from two solutions. - Bubbles are produced upon mixing two solutions. - The color of a substance changes over time. - A solution heats up upon mixing with another.
exothermic examples
- Acid and base are mixed, making test tube feel hot - A process with a calculated negative q - Wood burns in a fireplace
combustion rxn examples
2C2H6+7O2⟶4CO2+6H2O C+O2⟶CO2 2NO+O2⟶2NO22NO+OX2⟶2NOX2
produced in a chemical reaction is collected through water in a eudiometer. If the pressure in the eudiometer is 760.0 torr and the vapor pressure of water under the experimental conditions is 23.4 torr, what is the pressure (torr) of the gas
737
Predict the products of hydrochloric acid reacting with zinc metal.
H2 and ZnCl2
Which transition would correspond to the highest frequency of light emitted?
K = fleeting lavendar flame Na = brilliant yellow flame
What should you do if your Bunsen burner does not light after a few tries with the striker?
Turn off the gas cock for 10 seconds before trying again.
be able to balance equations
chemical reaction... question 5
non colligative property examples
color, density
A balloon is inflated outside on a cool morning. As the temperature rises, reaching its peak in the afternoon, the volume of the balloon will increase. . As the temperature cools down again in the evening, the volume of the balloon will decrease
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A hydrometer is a tool used to measure the density of a liquid relative to that of water
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At the freezing point, the liquid form of a substance is in equilibrium with the solid form of the substance.
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Which statements are true concerning a substance with a high specific heat?
- An example substance is water. - The substance cools down slowly after heating.
The freezing point of a 1 m solution of FeCl3 is expected to be lower than that of a 1 m solution of glucose. This is because FeCl3 is an electrolyte and has a larger van't Hoff factor compared with glucose.
- FeCl3FeClX3 dissociates into four ions - Therefore, the van't Hoff factor for FeCl3 is four. Glucose does not dissociate in water, giving a van't Hoff factor of one. - Freezing point depression is proportional to the van't Hoff factor, and therefore, this effect will be larger for FeCl3 . This will result in a lower freezing point for FeCl3 compared with glucose.
When using a properly stabilized balance, how should you ensure that you get the most accurate mass reading possible?
- Measure the mass of the sample at room temperature. - Close the side shields on the balance during reading.
endothermic examples
- Solid dissolves into solution, making ice pack feel cold - A process with a calculated positive q - Ice melts into liquid water
What is the freezing point (in degrees Celcius) of 3.72 kg of water if it contains 232.5 g of CaBr2CaBrX2 ? The freezing point depression constant for water is 1.86oC/m and the molar mass of CaBr2CaBrX2 is 199.89 g/mol.
-1.74 (molar mass of solute.. #4
value of R
.08206
Suppose that you add 26.1 g of an unknown molecular compound to 0.250 kg of benzene, which has a KfKf of 5.12oC/m. With the added solute, you find that there is a freezing point depression of 3.25oC compared to pure benzene. What is the molar mass (in g/mol) of the unknown compound?
164 g/mol - molar mass of solute.... #3
If 0.98 g of an unknown was dissolved in 10.30 g of solvent and the resulting solution has a molality of 0.45 m, what is the molar mass of the unknown?
211 g/mol molar mass of solute... #8
What mass, in grams, of NaCl needs to be added to 2.3 kg of water in order to create a solution with a freezing point of -6.1 °C? The freezing point depression constant of water is 1.86 ºC/m
220 - molar mass of... #5
not combustion rxn
2N2O5⟶4NO2+O22NX2OX5⟶4NOX2+OX2 CO2+4H2⟶CH4+2H2O
Visible light falls into wavelength ranges of 400-700 nm, for which 1 m=1×109 nm1 m=1×109 nm . The energy and wavelength of light are related by the equation E=hcλE=hcλ where EE is energy in Joules, hh is Planck's constant ( 6.626×10−34 J-s6.626×10−34 J-s ), cc is the speed of light ( 2.998×108 m/s2.998×108 m/s ), and λλ is the wavelength in m. If a visible light photon has a wavelength of 505.8 nm, what is the energy of the photon (in J)?
3.93 x 10^19 atomic spectra #8
best cylinder option for 5.75 mL of a sucrose solution
A 10 mL graduated cylinder with markings every 0.1 mL
When a Bunsen burner is properly adjusted, what should the flame look like?
Blue with no gap between the burner and the flame
Between flame tests, the nichrome wire is cleaned. What color should appear when a properly cleaned nichrome wire is introduced into the flame?
Light or faint yellow
.0350 m Mg is reacted with 10.00 mL of 6 HCl to produce aqueous MgCl2 and H2
Mg + 2HCl -> MgCl2 + H2 limiting reactant is the Mg (ideal gas law #8)
Hydrochloric acid and sodium hydroxide react to form _____________.
NaCl(aq) + H2O(l)
beaker
Pouring an approximate volume of liquid into a buret
arrow in a chemical rxn means
Substances on the reactants side are converted to the substances on the products side.
What is the general definition of heat capacity?
The change in heat required to change the temperature of something by one degree Celsius
What is the equivalence point of a titration?
When the amount of acid and base are equal.
Potassium hydrogen phthalate is ____________.
a primary standard (The weak acid potassium hydrogen phthalate, KHP, is a primary standard commonly used in titrations. A solution of KHP with known concentration is often titrated in order to determine the concentration of another solution.)
Which term describes a solution having a very well-known concentration of solute?
a standard solution
The indicator phenolphthalein is added to the _____________.
analyte (The indicator phenolphthalein is added to the analyte solution. The analyte is the solution underneath the buret, typically contained in a flask.)
What color is phenolphthalein when the solution is acidic?
colorless
stopcock placement - Filling the burette with titrant
completely closed
stopcock placement: Conditioning the burette with titrant
completely closed
stopcock placement - At the beginning of a titration
completely open
What occurs in endothermic reactions?
heat energy is absorbed
A reagent added to the analyte solution that changes color when the reaction is complete
indicator
What the relationship between frequency and wavelength of electromagnetic radiation?
inverse
The pressure is kept constant, while the temperature is decreased. What will happen to the volume?
it will decrease
stopcock placement - Close to the calculated equivalence point of a titration
partially open
One calorie (cal) is the amount of heat needed to _____________ the temperature of one gram of water one degree Celsius.
raise
The liquid dispensed from a burette is called ___________.
titrant
Process of slowly adding a solution to react with another solution and determine the concentration of one of the solutions based on the reaction between them
titration
colligative property examples
vapor pressure lowering, boiling point elevation, and freezing point depression - Colligative properties are dependent upon the amount of a solute, but not the nature of the solute. When salt is added to ice in order to lower the freezing point, for example, the magnitude of the effect is determined by the number of moles of salt added rather than the type of salt.
Suppose an air bubble is trapped in the eudiometer before starting the experiment. After the experiment is finished, the resulting value of R would be....
... too large
Suppose you are titrating a sulfuric acid solution of unknown concentration with a sodium hydroxide solution according to the equation H2SO4 + 2NaOH -> 2 H2O +NaSO4 If you require 29.63 mL of 0.775 M NaOHNaOH solution to titrate 190.7 mL of H2SO4HX2SOX4 solution, what is the concentration of the H2SO4HX2SOX4 solution?
.0602 - titration #8
How many moles of H2 can be formed if a 3.25 g sample of Mg reacts with excess HCl?
.134 create a formula: Mg+ 2 HCl -> MgCl2 +H2 - There is a 1:1 stoichiometric ratio between Mg and H2. convert the given mass of Mg to moles 3.25m Mg x 1 mol Mg/24.3 m Mg x 1 mol H2/1 mol Mg
How many grams of KOHKOH are needed to neutralize 14.7 mL of 0.17 M HClHCl in stomach acid?
.14 question 9 titration
Calculate the moles of ammonia present in a 5.050 g sample if the molar mass of ammonia is 17.030 g/mol.
.2965 (empirical formula question 7) - The molar mass of a compound is the mass of one of compound. Therefore, if you divide a mass of the compound by its molar mass, you will find how many moles of the compound are present.
Suppose you are titrating vinegar, which is an acetic acid solution of unknown strength, with a sodium hydroxide solution according to the equation HC2H3O2 + NaOH -> H2O + NaC2H3O2 If you require 31.26 mL of 0.1871 M NaOH solution to titrate 10.0 mL of HC2H3O2 solution, what is the molar concentration of acetic acid in the vinegar?
.585 look at titration question 6
Suppose you are titrating an acid solution with a base solution of known concentration. To calculate the concentration of the acid solution, use three steps.
1. use the delivered volume of base to reach the end point and the known concentration of the base solution to find the moles of base used 2. Use the molar ratio to find the moles of acid from the moles of base. 3. Divide the moles of acid by the volume of acid solution before the titration to find the concentration of acid.
A concentrated salt solution has a mass of 5.34 g for a 5.00 mL sample. What is the specific gravity of this solution? specific gravity = density of substance/density of water
1.07
Calculate the mass percent of a vinegar solution with a total mass of 98.53 g that contains 2.61 g of acetic acid.
2.58 - percent mass of a solution = mass of solute/mass of solution 2.61g/98.53g x 100
Suppose you are titrating an acid of unknown concentration with a standardized base. At the beginning of the titration, you read the base titrant volume as 1.08 mL. After running the titration and reaching the endpoint, you read the base titrant volume as 22.80 mL. What volume, in mL, of base was required for the titration?
21.7 mL - To find the volume of titrant used in any titration, subtract the starting volume reading from the final volume reading.
The temperature of a room is 21.4 °C. What is this temperature expressed in Kelvin (K)?
294
Suppose you mix 100.0 g of water at 21.7 oC with 75.0 g of water at 72.1 oC. What will be the final temperature of the mixed water, in oC?
43.3 - use final temp equation from equation sheet
Identify which balance was used to make each mass reading.
5.43 g = A balance with ±0.01 g tolerance 4.0000 = A balance with ±0.0001 g tolerance
What is the heat, q , in joules transferred by a chemical reaction to the reservoir of a calorimeter containing 95.0 g of dilute aqueous solution ( c=4.184 J/g⋅ºC) if the reaction causes the temperature of the reservoir to rise from 22.0 ºC to 24.5 ºC ?
994 q= (95 g)(4.184)(24.5-22.0)
best cylinder option for 18.5 mL of a NaCl solution
A 25 mL graduated cylinder with markings every 1 mL
best cylinder option for 36 mL of water
A 50 mL graduated cylinder with markings every 10 mL
Identify the common indicators that a chemical reaction has occurred.
A change in temperature, A color change, Bubbles being produced, Precipitate being formed
What appearance of an acidic analyte solution containing phenolphthalein indicates the endpoint of titration with a basic solution?
A persistent pale pink color throughout the solution.
Mass is conserved in an experiment if the sum of the individual component masses equals the mass of the mixture of the components
Conservation of mass means that all the mass you start with is still present. Thus, if the mass of the mixed components equals the sum of the masses of each individual component, mass is conserved.
A 7.298 g sample of copper reacts with oxygen, forming a copper oxide. The final mass of the copper oxide is 8.217 g. What is the formula of the copper oxide?
Cu2O (empirical formula question 6)
In a liquid with the same density as water...
Float in the same position as pure water
In a liquid that is less dense than water...
Float lower than position in pure water
In the reaction of magnesium metal with hydrochloric acid, how do you determine when the magnesium metal has reacted completely?
Gas bubbles are no longer produced. and the magnesium is gone
When exothermic reactions occur, ______________.
Heat energy is released.
delta arrow in a chem rxn
Heat is applied.
Magnesium reacts with oxygen in the air when lit with a bunsen burner. . Unlike other reactions, you should not look directly at this rxn
Magnesium burns in air when lit with a Bunsen burner. The reaction produces a lot of light energy so you should not look directly at it. Instead, watch it briefly out of the corner of your eye.
What practice will NOT help you make an accurate volume reading on a burette at the beginning of a titration?
Make sure that the meniscus starts exactly at 0.00 mL. - When reading the volume of titrant in a burette at the beginning of a titration, make sure to have the top of the liquid at eye level. You don't want an angled view to change your perspective of where the volume aligns compared to the markings. In particular, you need to align the bottom of the meniscus (curved top of the liquid) with the volume marking.
How can you improve your ability to see the indicator color change at the endpoint of a titration?
Place a piece of white paper under the analyte flask throughout the titration.
What should you do every time before you leave the lab?
Remove your labcoat, if you are wearing one, remove glasses, wash hands
When equal moles of an acid and a base are mixed, after reaction the two are compounds are said to be at the _______________.
Stoichiometric point
Suppose you mix two solutions in a test tube and the test tube becomes hot. This is a sign of a chemical reaction because chemical changes can release heat.
The heat generated in the test tube is a sign of a chemical reaction. Chemical reactions can either generate or consume heat. The mixture of the two solutions caused an exothermic reaction that released heat.
To measure out a volume of liquid, start by choosing the appropriate graduated cylinder and moving the bumper to the top of the graduated cylinder to protect it from breakage. Then, pour the liquid into the graduated cylinder until the bottom of the meniscus aligns with the desired volume marking when you look at the graduated cylinder from eye level
The proper way to read a graduated cylinder is to have the bottom of the meniscus line up with the volume marking when you view the graduated cylinder at eye level. Reading from above or below will lead to a reading that is too high or too low.
In the Ideal Gas Law lab, how is the temperature of the hydrogen gas determined?
The temperature of the water bath is measured after the reaction, which is assumed to be the same temperature as the gas.
plus sign in a chem rxn means
There are two separate substances on either the products side or the reactants side.
Before running a titration, you calculate the expected endpoint. However, when performing the experiment, you pass the expected endpoint with no visible color change. What is the most likely problem with the titration set-up?
There is not enough indicator in the analyte.
When a known quantity of compound, at a known concentration, is added to a known volume of another compound to determine the concentration of the latter, the process is referred to as _____________.
a titration
What parts are present in every chemical equation?
an arrow, at least one product, at least one reactant
Solution of an unknown concentration that has another solution slowly added to it
analyte
Consider the trendline on a graph of Mass vs. Volume of a solid or a liquid. What information can be obtained about the substance from the slope of this line?
density
The volume and temperature remain constant, while some of the gas is let out of the container. What will happen to the pressure?
it will decrease
If you double the wavelength of light, what happens to the energy of the photons?
it will decrease by one half
The pressure and volume are increased. What will happen to the temperature?
it will increase
The pressure and the temperature are both decreased by 50%. What will happen to the volume?
it will stay the same
A calorimeter measures the heat involved in reactions or other processes by measuring the temperature change of the materials surrounding the process. The calorimeter is insulated to prevent transfer of heat to outside the device
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In the context of a balanced chemical equation, a subscript is a number to the lower right of an element or ion within formula and it applies to only the part of the formula it follows. a coefficient is a number to the left of a formula and it applies to the entire formula is precedes. only coefficients should be added or changed when balancing chemical equations.
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Suppose you are given the mass of each element in a compound sample. To calculate the empirical formula, start by converting the mass of each element to moles using each element's molar mass. then, calculate the ratio between the elements by dividing the moles of each element by the smallest number of moles present.
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The equation to calculate density is d=m/v, where d is the density, m is the mass and v is the volume
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The relationship between pressure and volume of a gas is inverse so that as volume decreases, pressure increases
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When a vinegar and oil salad dressing separates into two layers, the oil floats on top of the vinegar. The density of the oil is less than the density of the vinegar
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When using the Tare function on a balance, start by placing the glassware on the balance. then press the Tare/Zero button to cancel out that mass. Finally, add your sample to the glassware and record the mass of your sample
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