Q: How many oxygen atoms are present in 2.60 g of $$CaCO_3$$? (Molar mass of $$CaCO_3 = 100.09$ g/mol)

$$4.70 \times 10$$^{22}$$ atoms

Q: If 0.346 mol of $$C_2H_6 is $$present, how many molecules of $$C_2H_6$$ are there?

$$2.08 \times 10$$^{23}$$ molecules

Q: Which of the following is the correct formula for calculating percent composition of an element in a compound?

$$\frac{\text{number of atoms of element} \times \text{atomic weight of element}}{\text{formula weight of compound}} \times 100$$

Q: Which of the following statements about the mole is correct?

One mole of any substance contains $$6.02 \times 10$$^{23}$$ particles.

Question 1

Which of the following statements about balancing chemical equations is correct?

Accepted Answer

You should only change the coefficients in front of chemical formulas to balance the equation.

Question 2

A sample of glucose ($$C_6H_{12}O_6$) has a mass of 18.0 g. How many moles of glucose are present in the sample? (Molar mass of C_6H$$_{12}$$O_6 = 180.12$ g/mol)

Accepted Answer

$$0.100$$ mol

Question 3

Which of the following is the correct balanced equation for the combustion of propane ($$C_3H_8) in $$oxygen?

Accepted Answer

$$C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$$

Question 4

A 5.00 g sample of a compound contains 2.06% hydrogen, 32.71% sulfur, and 65.23% oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

$$H_2SO_4$$

Question 5

How many oxygen atoms are present in 2.60 g of $$CaCO_3$$? (Molar mass of $$CaCO_3 = 100.09$ g/mol)

Accepted Answer

$$4.70 	imes 10$$^{22}$$ atoms

Question 6

Which of the following best describes a decomposition reaction?

Accepted Answer

A single reactant breaks apart to form two or more products.

Question 7

If 0.346 mol of $$C_2H_6 is $$present, how many molecules of $$C_2H_6$$ are there?

Accepted Answer

$$2.08 	imes 10$$^{23}$$ molecules

Question 8

A reaction requires 5.00 mmol of NaCl. How many grams of NaCl should be weighed out? (Molar mass of NaCl = 58.44 g/mol)

Accepted Answer

$$0.292 g$$

Question 9

Which of the following is the correct mole ratio for the reaction $$2H_2 + O_2$ \rightarrow 2H_2O$$ relating $$H_2 to$$ $$O_2$$?

Accepted Answer

$$2$$ mol $$H_2$$ : $$1$$ mol $$O_2$$

Question 10

A 7.24 x $$10^9$$ atom sample of lead (Pb) is present. What is the mass of this sample? (Atomic mass of Pb = 207.2 g/mol, Avogadro's number = $$6.02 	imes 10$$^{23}$$)

Accepted Answer

$$2.49 	imes 10$$^{-12}$$ g

Question 11

Which of the following best describes a limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed and determines the amount of product formed.

Question 12

A compound has an empirical formula of $$CH_2O$$ and a molar mass of 180 g/mol. What is its molecular formula?

Accepted Answer

$$C_6H_{12}O_6$

Question 13

In the reaction $$2Al(s) + 6HCl(aq) \rightarrow 2AlCl_3(aq) + 3H_2(g)$$, how many moles of $$H_2$$ are produced from 0.50 mol of $$Al$$?

Accepted Answer

$$0.75$$ mol

Question 14

A student recovers 1.12 g of $$Zn(NO_3$)_2$$ from a reaction where the theoretical yield is 1.39 g. What is the percent yield?

Accepted Answer

$$80.6\%$$

Question 15

Which of the following is the correct formula for calculating percent composition of an element in a compound?

Accepted Answer

$$\frac{	ext{number of atoms of element} 	imes 	ext{atomic weight of element}}{	ext{formula weight of compound}} 	imes 100$$

Question 16

If 3.81 g of $$C_2H_6 is $$burned in excess oxygen, how many grams of $$CO_2$$ are produced? (Molar mass $$C_2H_6 = 30.07 g/$$mol, $$CO_2 = 44.01$ g/mol, reaction: 2C_2H_6 + 7O_2$$ \rightarrow 4CO_2 + 6H_2O$$)

Accepted Answer

$$5.58 g$$

Question 17

Which of the following is a correct example of a single replacement (displacement) reaction?

Accepted Answer

$$Fe(s) + $$CuSO_4$$(aq) \rightarrow $$FeSO_4$$(aq) + Cu(s)$$

Question 18

A hydrate of $$FeSO_4$$ contains 7 water molecules per formula unit. What is the molar mass of $$FeSO_4$$ \cdot 7H_2O$$? (Atomic masses: Fe = 55.85, S = 32.07, O = 16.00, H = 1.01)

Accepted Answer

$$278.02 g/$$mol

Question 19

Which of the following statements about the mole is correct?

Accepted Answer

One mole of any substance contains $$6.02 	imes 10$$^{23}$$ particles.

Stoichiometry: Calculations with Chemical Formulas and Equations

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