Q: A sample contains $$4.55$$ millimoles of zinc. How many zinc atoms are present? ($$N_A = 6.022 \times 10$$^{23}$$\ \mathrm{mol}^{-1})$$

$$2.74 \times 10$$^{21}$$ atoms

Q: How many atoms of oxygen are present in $$23.0\ \mathrm{mg} of$$ $$\mathrm{Ga_2$($$HPO_4$$)_3}$$? (Molar mass $$= 451.32\ \mathrm{g/mol}$$, $$N_A = 6.022 \times 10$$^{23}$$)

$$1.47 \times 10$$^{22}$$ atoms

Question 1

Which of the following statements about the dissolution of solid sodium hydroxide (NaOH) in water is correct, based on the observed temperature increase and the chemical species present after mixing?

Accepted Answer

The process is exothermic, resulting in increased kinetic energy, and produces a homogeneous mixture of ions.

Question 2

Convert $$45.3\ ^\circ\mathrm{F} to $$Kelvin ($$K). $$Use the following equations:

$$T_{\mathrm{C}} = \frac{5}{9}(T_{\mathrm{F}} - 32)$$

$$T_{\mathrm{K}} = T_{\mathrm{C}} + 273.15$$

Accepted Answer

$$280.2\ \mathrm{K}$$

Question 3

Which law is being tested when comparing the masses of oxygen that combine with a fixed mass of osmium in two different compounds?

Accepted Answer

Law of Multiple Proportions

Question 4

A sample contains $$4.55$$ millimoles of zinc. How many zinc atoms are present? ($$N_A = 6.022 	imes 10$$^{23}$$\ \mathrm{mol}^{-1})$$

Accepted Answer

$$2.74 	imes 10$$^{21}$$ atoms

Question 5

Which of the following is the correct empirical formula for a compound containing $$2.677\ \mathrm{g} of Ba $$and $$3.115\ \mathrm{g} of Br$$?

Accepted Answer

$$\mathrm{$$BaBr_2$$}$$

Question 6

Which of the following statements from Dalton’s atomic theory is inconsistent with the existence of isotopes such as boron-11 and carbon-12?

Accepted Answer

All atoms of a given element are identical in mass and properties.

Question 7

What is the oxidation state of manganese in $$\mathrm{Mn_2O_7}$$, and what is the ratio of the oxidation state of elemental manganese to that in $$\mathrm{Mn_2O_7}$$?

Accepted Answer

Oxidation state in $$\mathrm{Mn_2O_7} is$$ $$+7$$; ratio is $$0 : 7$$

Question 8

Which of the following is the correct name for $$\mathrm{Cu(NO_3$)_2 \cdot 8H_2O}$$?

Accepted Answer

Copper(II) nitrate octahydrate

Question 9

How many protons, neutrons, and electrons are present in $$^{70}\mathrm{Ga}^{3+}$$?

Accepted Answer

Protons: $$31$$, Neutrons: $$39$$, Electrons: $$28$$

Question 10

Which of the following is the correct formula for triphosphorus heptachloride?

Accepted Answer

$$\mathrm{P_3Cl_7}$$

Question 11

Calculate the mass of $$2.45$$ moles of aluminum. (Atomic mass of Al $$= 26.98\ \mathrm{g/mol})$$

Accepted Answer

$$66.1\ \mathrm{g}$$

Question 12

Which of the following best describes sodium sulfate ($$\mathrm{Na_2SO_4}$$)?

Accepted Answer

An ionic compound composed of sodium cations and sulfate anions

Question 13

What is the molar mass of $$\mathrm{Ga_2$($$HPO_4$$)_3}$$? (Atomic masses: Ga = $$69.72$$, H = $$1.01$$, P = $$30.97$$, O = $$16.00)$$

Accepted Answer

$$451.32\ \mathrm{g/mol}$$

Question 14

Which of the following elements is a metalloid most chemically similar to an element with $$Z = 14$$ and $$A = 30$$?

Accepted Answer

Germanium (Ge)

Question 15

How many $$\mu\mathrm{g} of $$zinc are present in $$6.55 	imes 10$$^{21}$$ zinc atoms? (Atomic mass of Zn = 65.38$$\ \mathrm{g/mol}$$, N_A = 6.022$$ 	imes $$10^{23}$$\ \mathrm{mol}^{-1}$$)

Accepted Answer

$$712\ \mu\mathrm{g}$$

Question 16

Which of the following is the correct balanced chemical equation for the reaction of solid lead(II) sulfide with aqueous hydrobromic acid to form solid lead(II) bromide and dihydrogen monosulfide gas?

Accepted Answer

$$\mathrm{PbS(s) + 2HBr(aq) \rightarrow $$PbBr_2$$(s) + H_2S(g)}$$

Question 17

Which of the following pairs are representative elements that form ions with a $$2+$$ charge, and what family do they belong to?

Accepted Answer

Magnesium (Mg) and Calcium (Ca); Alkaline Earth Metals

Question 18

What is the mass percent of phosphorus in $$\mathrm{Ga_2$($$HPO_4$$)_3}$$? (Molar mass from previous question: $$451.32\ \mathrm{g/mol}$$, P atomic mass $$= 30.97)$$

Accepted Answer

$$20.6\%$$

Question 19

How many atoms of oxygen are present in $$23.0\ \mathrm{mg} of$$ $$\mathrm{Ga_2$($$HPO_4$$)_3}$$? (Molar mass $$= 451.32\ \mathrm{g/mol}$$, $$N_A = 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.47 	imes 10$$^{22}$$ atoms

General Chemistry I: Practice Midterm Guidance (Chapters 1–3)

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