Q: How many molecules are present in $$0.00210 g of $$cesium chloride ($$\mathrm{CsCl}$$)? (Molar mass of $$\mathrm{CsCl} = 168.36 g/$$mol, $$N_A = 6.022 \times 10$$^{23}$$ mol$$^{-1}$$)

$$7.51 \times 10$$^{18}$$ molecules

Question 1

Which of the following statements best describes Rutherford's gold foil experiment and its significance for atomic theory?

Accepted Answer

It demonstrated that atoms are mostly empty space with a small, dense, positively charged nucleus at the center.

Question 2

A neutral atom of $$^{81}\mathrm{Br}$$ has how many protons, neutrons, and electrons?

Accepted Answer

Protons: 35, Neutrons: 46, Electrons: 35

Question 3

Which of the following is the correct chemical formula for ammonium sulfate, and what is the charge on the sulfate ion?

Accepted Answer

$$\mathrm{(NH_4$)_2SO_4}$$; sulfate ion charge = $$-2$$

Question 4

Which of the following acids is NOT a strong acid and therefore a weak electrolyte in aqueous solution?

Accepted Answer

$$\mathrm{HF}$$

Question 5

Calculate the average atomic mass of magnesium given the following isotopic abundances: $$^{24}\mathrm{Mg} (78.99$$%, 23.9850 amu), $$^{25}\mathrm{Mg} (10.00$$%, 24.9858 amu), $$^{26}\mathrm{Mg} (11.01$$%, 25.9826 amu).

Accepted Answer

$$24.31$$ amu

Question 6

Which of the following best describes the process for predicting the products of a double-displacement reaction between aqueous solutions of sodium sulfate and barium chloride?

Accepted Answer

Exchange the cations and anions to form barium sulfate and sodium chloride, then use solubility rules to determine phases.

Question 7

How many molecules are present in $$0.00210 g of $$cesium chloride ($$\mathrm{CsCl}$$)? (Molar mass of $$\mathrm{CsCl} = 168.36 g/$$mol, $$N_A = 6.022 	imes 10$$^{23}$$ mol$$^{-1}$$)

Accepted Answer

$$7.51 	imes 10$$^{18}$$ molecules

Question 8

Which of the following is the correct balanced equation (with phases) for the reaction between aqueous lead(II) nitrate and aqueous cesium chloride?

Accepted Answer

$$\mathrm{Pb(NO_3$)_2(aq) + 2CsCl(aq) \rightarrow 2CsNO_3(aq) + $$PbCl_2$$(s)}$$

Question 9

A sample contains $$8.6 	imes 10$$^{21}$$ molecules of lead(II) nitrate. How many moles of lead(II) nitrate are present? (N_A = 6.022$$ 	imes $$10^{23}$$ mol$$^{-1})$$

Accepted Answer

$$0.0143$$ mol

Question 10

Which of the following best describes the difference between empirical and molecular formulas?

Accepted Answer

The empirical formula shows the simplest whole-number ratio of elements, while the molecular formula shows the actual number of atoms of each element in a molecule.

Question 11

Which of the following compounds is a binary molecular compound?

Accepted Answer

$$\mathrm{CO_2$}$$

Question 12

How many grams of $$\mathrm{NH_3$}$$ are produced from $$2.56 g of$$ $$\mathrm{N_2$}$$ according to the reaction $$\mathrm{N_2$ + 3H_2 \rightarrow 2NH_3}$$? (Molar masses: $$\mathrm{N_2$} = 28.014 g/$$mol, $$\mathrm{NH_3$} = 17.031 g/$$mol)

Accepted Answer

$$3.11 g$$

Question 13

Which of the following is the correct name for $$\mathrm{H_3PO_4}$$?

Accepted Answer

Phosphoric acid

Question 14

A student mixes $$785 mg of $$lithium carbonate ($$\mathrm{Li_2CO_3}) $$with $$1000 mg of $$phosphoric acid ($$\mathrm{H_3PO_4}). $$Which reactant contains the greater number of molecules? (Molar masses: $$\mathrm{Li_2CO_3} = 73.89 g/$$mol, $$\mathrm{H_3PO_4} = 98.00 g/$$mol)

Accepted Answer

Phosphoric acid ($$\mathrm{H_3PO_4})$$

Question 15

Which of the following is the correct molar mass (to two decimal places) for copper(II) bromide, $$\mathrm{$$CuBr_2$$}$$? (Atomic masses: Cu = 63.55, Br = 79.90)

Accepted Answer

$$223.35 g/$$mol

Question 16

Which of the following is a correct statement about the solubility of ionic compounds in water?

Accepted Answer

Compounds containing nitrate ($$\mathrm{NO_3$^-}) $$are always soluble in water.

Question 17

Which of the following is the correct scientific notation for $$0.000560$$?

Accepted Answer

$$5.60 	imes 10$$^{-4}$$

Question 18

A reaction produces $$36.4 g of $$HCN gas, but the theoretical yield is $$52.1 g. $$What is the percent yield?

Accepted Answer

$$69.8\%$$

Question 19

Which of the following is the correct prefix multiplier for 'nano-'?

Accepted Answer

$$1 	imes 10$$^{-9}$$

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