ochem lab review

This week you will be using a 2 g of a 50/50 mixture of benzoic acid and benzophenone. If you have a 2 g mixture that is 50% benzoic acid and 50% benzophenone, how many moles of benzoic acid do you have? Include units in your answer

0.008 moles mole=1g/122g(mol) (molar mass of benzoic acid)= 0.008

How many moles of 1-bromobutane do we expect to make in this reaction? Hint: Determine what is the limiting reagent.

0.11 NaBr and 1-butanol are both in roughly 0.11 mol therefore they are the limiting reagents, so we expect 0.11 mol of 1-bromobutane to be formed.

For this reaction you will be using 10 mL of 1-butanol. Calculate the number of moles of 1-butanol. Round your answer up to the second decimal place and include units in your answer.

0.11 mol Density of 1-butanol = 0.81 g/mL First, we need to convert from mL to grams so we need to use density here: 10 mL x (0.81 g/mL) = 8.1 g Now that we are in grams, we can use MW which is in units of g/mol to convert to moles: 8.1 g / (74.12 g/mol) = 0.11 moles

How many grams of NaOH is there in 124 mL of a 0.04M solution of aqueous NaOH?

0.2 g convert mL to L: 125 mL x (1/1000) = 0.125 L Calculate Moles: 0.125 L x (0.04 mol/L) = 0.005 moles Calculate grams: 0.005 mol x (40 g/mol) = 0.2 g NaOH

In question 1, you calculated how many moles of 1-butanol you will be working with. How many equivalents of NaBr will you be using with respect to 1-butanol? Hint: Equivalents are a simplified ratio of the number of moles we are using. For example, if I have 10 mol of NaBr and 5 mol of 1-butanol, then I have 2 equivalents of NaBr and 1 equivalent of 1-butanol. (2:1 ratio of NaBr:1-butanol)

1 equivalents of NaBr and 1 equivalent of 1-butanol Because we have 0.11 mol of NaBr and 0.11 mol of 1-butanol, we have 1 equivalent of NaBr and 1 equivalent of 1-butanol

This week you will be using 15 mL of 2.5 M aqueous sodium hydroxide solution. How many grams of sodium hydroxide are present in the 15 mL solution of 2.5 M aqueous sodium hydroxide? Include units in your answer. Hint: you will need to use the molecular weight of sodium hydroxide to convert from moles to grams

1.5 g convert mL to L: 15 mL = 0.015 L then use volume and molarity to calculate moles: 0.015 L x 2.5 mol/L = 0.0375 mol then use molecular weight of NaOH to convert mol to grams: 0.0375 mol x 40 g/mol = 1.5 g

ONLY melting point and NOT thin layer chromatography can be used to confirm the purity/identity of our recrystallized unknown molecule.

False

Column chromatography works just like TLC. However, you load the sample on the top of the column and it travels down to the bottom. The most nonpolar molecule elutes out of the column first. Which molecule do you expect to elute off the column first?

Methyl Benzoate

Silica gel is an amorphous powder that we will be using to pack the column for our experiment. Silica gel is a carcinogen that gets permanently trapped in your lungs if inhaled. NEVER pour the dry silica gel powder outside of a fume hood. ALWAYS pour the silica gel powder inside the fume hood.

TRUE

Which of the following requirements will NOT results in a successful fractional distillation?

Uniform heating of the column

Which of the following results from melting point analysis indicate that you have an impure compound?

a lower melting point than expected and a broad melting point range

This week you will be doing an extraction using diethyl ether and aqueous sodium hydroxide solution which are two immiscible liquids. Which liquid will from the top layer?

diethyl ether

n TLC, if you have too concentrated of a sample, after you run the TLC plate in the chamber you will see a long streak across the TLC plate instead of a nice resolved spot. How do you dilute your sample?

dilute you initial sample by adding more solvent and re-run the sample on a new TLC plate

Based on the following equation which type of reaction occurs when 2-methyl-2-chlorobutane is reacted with water/2-propanol? Elimination, Substitution or both?

elimination and substitution

What is the correct placement of the thermometer bulb in the setup?

level with the sidearm

Imagine you are analyzing a TLC plate that you just pulled out of the chamber. You notice that it has one spot stuck on the baseline of the TLC plate. To get your spot to move up towards the top of the plate, do you make your eluant more polar or less polar?

make a more polar eluant

The following solvents will be used in our fractional and simple distillations: toluene, acetone, cyclohexane, and 1,4-dioxane. If you have any waste associated from these chemicals, which waste container is most appropriate for their disposal?

non-halogenated organic waste

When setting up your fractional distillation, where should you place the utility clamps?

one on the neck of the round bottom flask and one on the narrow condenser

What peaks do you expect to see in the IR spectrum of your product of the dehydration of cyclohexanol ?

peaks that correspond to Csp3-H bond stretching, peaks that correspond to Csp2-H bond stretching peaks that correspond to C=C bond stretching

Which of the following steps should you take if your crystals do not form?

seeding and scratching

When selecting for a solvent to use in your recrystallization, you want to find a solvent that...

that solubilizes the solute (your compound) when the solution is heated

Safety Q: If you get organic materials on your hands, you should...

wash your hands with soap and warm water

When should you change your receiving flask?

when the begins to rise or fall after the first plateau and when the temperature reaches the second plateau

his week you will be heating cyclohexanol and 9 M sulfuric acid in a 25 mL round bottom flask that is setup up for fractional distillation. How will you know to stop heating your flask equipped for fractional distillation?

you will stop heating when only about 2.5 mL remains in the flask you are heating