Q: You are given a metal cylinder and asked to determine its density. You find its mass to be 45.0 g. When you place it in a graduated cylinder containing 25.0 mL of water, the water level rises to 30.5 mL. What is the density of the metal?

$$\text{Density} = \frac{45.0\ \text{g}}{5.5\ \text{mL}} = 8.18\ \text{g/mL}$$

Q: A student is given an unknown hydrated salt sample. The sample weighs 5.00 g before heating and 3.20 g after heating. What is the mass percent of water in the sample?

$$\frac{1.80\ \text{g}}{5.00\ \text{g}} \times 100\% = 36.0\%$$

Q: A student is given a hydrated salt with the formula $$\text{CuSO}_4 \cdot 5\text{H}_2\text{O}. $$What is the theoretical mass percent of water in this compound? (Molar masses: CuSO$$_4 = 159.6 g/$$mol, H$$_2O = 18.0 g/$$mol)

$$\frac{5 \times 18.0}{159.6 + 5 \times 18.0} \times 100\% = 36.1\%$$

Q: In a titration experiment, 0.500 g of KHP (potassium hydrogen phthalate, molar mass = 204.2 g/mol) is titrated with NaOH. How many moles of KHP are used?

$$\frac{0.500\ \text{g}}{204.2\ \text{g/mol}} = 0.00245\ \text{mol}$$

Q: A student titrates 25.00 mL of HCl with 0.100 M NaOH. The reaction is $$\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}. If it $$takes 30.00 mL of NaOH to reach the endpoint, what is the molarity of the HCl solution?

$$\frac{0.100 \times 30.00}{25.00} = 0.120\ \text{M}$$

Q: A student determines the mass of an empty flask to be 50.00 g. After adding an unknown liquid, the mass is 62.35 g. If the volume of the liquid is 10.0 mL, what is the density of the liquid?

$$\frac{62.35 - 50.00}{10.0} = 1.24\ \text{g/mL}$$

Q: A student titrates 0.250 g of KHP with NaOH. If it takes 15.00 mL of NaOH to reach the endpoint and the molarity of NaOH is unknown, what is the molarity of NaOH? (KHP molar mass = 204.2 g/mol)

$$\text{Molarity} = \frac{0.250/204.2}{0.01500} = 0.0816\ \text{M}$$

Question 1

A student heats a blue crystalline solid and observes that it turns white and releases water vapor. Which of the following best describes the type of change and the evidence supporting your answer?

Accepted Answer

It is a chemical change; the release of water vapor and color change indicate a new compound is formed.

Question 2

You are given a metal cylinder and asked to determine its density. You find its mass to be 45.0 g. When you place it in a graduated cylinder containing 25.0 mL of water, the water level rises to 30.5 mL. What is the density of the metal?

Accepted Answer

$$	ext{Density} = \frac{45.0\ 	ext{g}}{5.5\ 	ext{mL}} = 8.18\ 	ext{g/mL}$$

Question 3

A student is given an unknown hydrated salt sample. The sample weighs 5.00 g before heating and 3.20 g after heating. What is the mass percent of water in the sample?

Accepted Answer

$$\frac{1.80\ 	ext{g}}{5.00\ 	ext{g}} 	imes 100\% = 36.0\%$$

Question 4

A student is given a hydrated salt with the formula $$	ext{CuSO}_4 \cdot 5	ext{H}_2	ext{O}. $$What is the theoretical mass percent of water in this compound? (Molar masses: CuSO$$_4 = 159.6 g/$$mol, H$$_2O = 18.0 g/$$mol)

Accepted Answer

$$\frac{5 	imes 18.0}{159.6 + 5 	imes 18.0} 	imes 100\% = 36.1\%$$

Question 5

A student heats 2.50 g of a hydrated salt and obtains 1.60 g of the anhydrous salt. What is the empirical formula if the anhydrous salt is MgCl$$_2 ($$molar mass = 95.2 g/mol) and the water lost is 0.90 g?

Accepted Answer

MgCl$$_2$$·6H$$_2O$$

Question 6

In a titration experiment, 0.500 g of KHP (potassium hydrogen phthalate, molar mass = 204.2 g/mol) is titrated with NaOH. How many moles of KHP are used?

Accepted Answer

$$\frac{0.500\ 	ext{g}}{204.2\ 	ext{g/mol}} = 0.00245\ 	ext{mol}$$

Question 7

A student titrates 25.00 mL of HCl with 0.100 M NaOH. The reaction is $$	ext{HCl} + 	ext{NaOH} ightarrow 	ext{NaCl} + 	ext{H}_2	ext{O}. If it $$takes 30.00 mL of NaOH to reach the endpoint, what is the molarity of the HCl solution?

Accepted Answer

$$\frac{0.100 	imes 30.00}{25.00} = 0.120\ 	ext{M}$$

Question 8

Which of the following is NOT evidence of a chemical change?

Accepted Answer

Dissolving sugar in water

Question 9

A student determines the mass of an empty flask to be 50.00 g. After adding an unknown liquid, the mass is 62.35 g. If the volume of the liquid is 10.0 mL, what is the density of the liquid?

Accepted Answer

$$\frac{62.35 - 50.00}{10.0} = 1.24\ 	ext{g/mL}$$

Question 10

A hydrated salt sample contains 2.00 g of salt and 0.50 g of water. What is the empirical formula if the anhydrous salt is CaCl$$_2 ($$molar mass = 111.0 g/mol) and the water lost is 0.50 g?

Accepted Answer

CaCl$$_2$$·2H$$_2O$$

Question 11

Which of the following best describes the process of determining the density of an irregularly shaped solid?

Accepted Answer

Measure the mass and calculate the volume by water displacement.

Question 12

A student titrates 0.250 g of KHP with NaOH. If it takes 15.00 mL of NaOH to reach the endpoint and the molarity of NaOH is unknown, what is the molarity of NaOH? (KHP molar mass = 204.2 g/mol)

Accepted Answer

$$	ext{Molarity} = \frac{0.250/204.2}{0.01500} = 0.0816\ 	ext{M}$$

Question 13

Which of the following is a physical change?

Accepted Answer

Boiling water to produce steam

Question 14

A student mixes two clear solutions and observes the formation of a cloudy white solid. What type of change has occurred and what is the evidence?

Accepted Answer

Chemical change; formation of a precipitate

Question 15

A student is given 10.0 mL of an unknown HCl solution and titrates it with 0.200 M NaOH. If it takes 12.5 mL of NaOH to reach the endpoint, what is the molarity of the HCl solution?

Accepted Answer

$$\frac{0.200 	imes 12.5}{10.0} = 0.250\ 	ext{M}$$

Question 16

Which of the following best describes how to determine the mass percent of water in a hydrated salt?

Accepted Answer

Subtract the mass after heating from the mass before heating, divide by the initial mass, and multiply by 100%.

Question 17

A student is given a sample of hydrated salt. After heating, the mass of the sample decreases from 3.00 g to 2.40 g. If the anhydrous salt is FeCl$$_3 ($$molar mass = 162.2 g/mol), how many moles of water were lost?

Accepted Answer

$$\frac{3.00 - 2.40}{18.0} = 0.0333\ 	ext{mol}$$

Question 18

A student dissolves 2.00 g of NaCl in 50.0 mL of water. Which of the following best describes the type of change and the evidence?

Accepted Answer

Physical change; NaCl dissolves but no new substance is formed.

General Chemistry Lab Techniques and Calculations: Midterm Review Notes

Guida di studio - Domande di pratica

Study guide - Flashcard