Q: A blimp contains 495 kg of helium. How many helium atoms does it contain? (Molar mass of He = 4.00 g/mol, Avogadro's number $$= 6.022 \times 10$$^{23}$$ atoms/mol)

$$\mathrm{7.45 \times 10$$^{28}$$}$$

Question 1

Which of the following is the correct chemical formula for a compound containing three sulfur atoms for every one carbon atom?

Accepted Answer

S3C

Question 2

How many oxygen atoms are present in one formula unit of $$\mathrm{Ti_3$(PO_4$)_4}$$?

Accepted Answer

16

Question 3

When aqueous solutions of barium nitrate and potassium sulfate are mixed, which precipitate forms?

Accepted Answer

BaSO4 (s)

Question 4

Which set of reactants will form a solid precipitate when mixed in aqueous solution?

Accepted Answer

Na2CO3 (aq) & CaCl2 (aq)

Question 5

What is the net ionic equation for the reaction between $$\mathrm{Pb(C_2H_3O_2)_2} (aq) $$and KBr (aq)?

Accepted Answer

$$\mathrm{Pb$$^{2+}$$ (aq) + 2 Br^- (aq) \rightarrow $$PbBr_2$$ (s)}$$

Question 6

A student mixes 2.55 mol of sulfur with excess fluorine gas according to the reaction $$\mathrm{S (s) + 3 F_2$ (g) \rightarrow SF_6$ (g)}. $$How many moles of $$\mathrm{F_2$}$$ are required to react completely with the sulfur?

Accepted Answer

7.65 mol

Question 7

What is the theoretical yield of sodium chloride when 55.0 g of sodium reacts with 67.2 g of chlorine gas according to $$\mathrm{2 Na (s) + Cl_2$ (g) \rightarrow 2 NaCl (s)}$$?

Accepted Answer

111 grams

Question 8

A reaction has a theoretical yield of 22.8 g. When the reaction is carried out, 15.1 g of product is obtained. What is the percent yield?

Accepted Answer

$$\mathrm{66.2\%}$$

Question 9

A compound is decomposed in the laboratory and produces 1.40 g of nitrogen and 0.20 g of hydrogen. What is the empirical formula of the compound?

Accepted Answer

NH2

Question 10

Which of the following compounds is insoluble in water?

Accepted Answer

Ba3(PO4)2

Question 11

Consider the reaction $$\mathrm{3A + 4B \rightarrow 2C}. If 11 $$mol of A combine with 16 mol of B, how many moles of C can be formed?

Accepted Answer

8.0 mol

Question 12

Which of the following best describes a precipitation reaction?

Accepted Answer

double displacement

Question 13

Which of the following reactions is a redox reaction?

Accepted Answer

$$\mathrm{Al (s) + 3 Ag^+ (aq) \rightarrow Al$$^{3+}$$ (aq) + 3 Ag (s)}$$

Question 14

A blimp contains 495 kg of helium. How many helium atoms does it contain? (Molar mass of He = 4.00 g/mol, Avogadro's number $$= 6.022 	imes 10$$^{23}$$ atoms/mol)

Accepted Answer

$$\mathrm{7.45 	imes 10$$^{28}$$}$$

Question 15

Which of the following best represents the balanced molecular equation for the reaction between HBr(aq) and NaOH(aq)?

Accepted Answer

$$\mathrm{HBr (aq) + NaOH (aq) \rightarrow H_2O (l) + NaBr (aq)}$$

Question 16

A sample of 127 grams of $$\mathrm{Ca($$ClO_3$$)_2} is $$analyzed. How many grams of chlorine are present in the sample? (Molar mass: $$\mathrm{Ca($$ClO_3$$)_2} = 206.98 g/$$mol, Cl = 35.45 g/mol)

Accepted Answer

43.5 grams

Question 17

Which of the following is the correct empirical formula for a compound with a molar mass of 120.10 amu and an empirical formula of CH2O?

Accepted Answer

C4H8O4

Question 18

A reaction mixture contains 6 mol A, 8 mol B, and 10 mol C for the reaction $$\mathrm{2A + 3B + C \rightarrow 2D}. $$What is the limiting reactant?

Accepted Answer

B

Question 19

Which of the following is the correct balanced equation for the combustion of $$\mathrm{C_4H_9OH}$$?

Accepted Answer

$$\mathrm{C_4H_9OH (l) + 6 O_2$ (g) \rightarrow 4 CO_2$ (g) + 5 H_2O (l)}$$

Question 20

A chemist allows 61.5 grams of $$\mathrm{SO_3$}$$ and 11.2 grams of $$\mathrm{H_2O} to $$react according to $$\mathrm{SO_3$ (g) + H_2O (l) \rightarrow H_2SO_4 (aq)}. $$When the reaction is finished, 54.9 grams of $$\mathrm{H_2SO_4}$$ are collected. What is the percent yield?

Accepted Answer

89.0%

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