Q: How many atoms are present in 2.49 moles of sodium ($$\mathrm{Na}$$)? ($$N_A = 6.022 \times 10$$^{23}$$\ \mathrm{mol}^{-1})$$

$$1.50 \times 10$$^{24}$$ atoms

Q: Heated lithium atoms emit photons with an energy of $$2.961 \times 10$$^{-19}$$\ \mathrm{J}. $$What is the wavelength of one of these photons? ($$c = 3.00 \times 10^8$\ \mathrm{m/s}$$, $$h = 6.626 \times 10$$^{-34}$$\ \mathrm{J\cdot s})$$

$$6.72 \times 10$$^{-7}$$\ \mathrm{m}$$

Question 1

Which of the following best classifies air at sea level?

Accepted Answer

Homogeneous mixture

Question 2

Which of the following is a chemical change?

Accepted Answer

Baking a cake

Question 3

Convert 47.0 K to degrees Fahrenheit ($$^\circF). $$Use the formulas: $$^\circ C = K - 273.15$$ and $$^\circ F = \frac{9}{5}(^\circ C) + 32.$$

Accepted Answer

$$-370^\circ F$$

Question 4

How many protons, neutrons, and electrons are in $$^{43}_{20}\mathrm{Ca}$$?

Accepted Answer

20 protons, 23 neutrons, 20 electrons

Question 5

A sample of magnesium contains 79% $$^{24}Mg$$, 10% $$^{25}Mg$$, and 11% $$^{26}Mg. $$What is the average atomic mass of magnesium? (Round to two decimal places.)

Accepted Answer

$$24.32\ \mathrm{amu}$$

Question 6

Which of the following elements is a halogen?

Accepted Answer

Bromine

Question 7

How many atoms are present in 2.49 moles of sodium ($$\mathrm{Na}$$)? ($$N_A = 6.022 	imes 10$$^{23}$$\ \mathrm{mol}^{-1})$$

Accepted Answer

$$1.50 	imes 10$$^{24}$$ atoms

Question 8

A 340 g sample of copper reacts with oxygen to produce 605 g of copper(II) oxide. What mass of copper is present in a 420 g sample of copper(II) oxide? (Assume the same composition.)

Accepted Answer

236.4 g

Question 9

What is the percent composition of carbon in $$\mathrm{C}_4\mathrm{H}_6\mathrm{O}_4$$? (Atomic masses: C = 12.01, H = 1.01, O = 16.00)

Accepted Answer

49.0%

Question 10

What is the formula for calcium phosphate?

Accepted Answer

$$\mathrm{Ca}_3(\mathrm{PO}_4)_2$$

Question 11

Balance the following equation: $$\mathrm{Al} + \mathrm{HCl} \rightarrow \mathrm{H}_2 + \mathrm{AlCl}_3$$

Accepted Answer

$$2\mathrm{Al} + 6\mathrm{HCl} \rightarrow 3\mathrm{H}_2 + 2\mathrm{AlCl}_3$$

Question 12

If 35.5 g of aluminum reacts with 15.0 g of $$\mathrm{O}_2$$ according to $$4\mathrm{Al} + 3\mathrm{O}_2 \rightarrow 2\mathrm{Al}_2\mathrm{O}_3$$, how many moles of $$\mathrm{Al}_2\mathrm{O}_3$$ can be formed? (Al: 26.98 g/mol, $$\mathrm{O}_2$$: 32.00 g/mol)

Accepted Answer

0.329 mol

Question 13

A reaction should theoretically produce 23.0 g of NaCl, but only 21.5 g is actually produced. What is the percent yield?

Accepted Answer

93.5%

Question 14

What is the molarity of a solution containing 8.30 g of $$\mathrm{MgSO}_4$$ dissolved in 600.0 mL of solution? (Molar mass $$\mathrm{MgSO}_4 = 120.37 g/$$mol)

Accepted Answer

0.115 M

Question 15

How many mL of a 2.50 M KOH solution are needed to prepare 350 mL of 0.650 M KOH?

Accepted Answer

91.0 mL

Question 16

Given the reaction $$\mathrm{CaCl}_2(aq) + 2\mathrm{AgNO}_3(aq) \rightarrow 2\mathrm{AgCl}(s) + \mathrm{Ca(NO}_3)_2(aq)$$, which product forms a precipitate?

Accepted Answer

$$\mathrm{AgCl}$$

Question 17

A 300.0 mL sample of $$\mathrm{N}_2(g) is at 1 $$atm and 43 $$^\circC. If $$the temperature is decreased to $$-23^\circC at $$constant pressure, what is the new volume? (Use $$V_1$$/$$T_1$$ = $$V_2$$/$$T_2$$ with temperatures in Kelvin.)

Accepted Answer

210 mL

Question 18

How much heat is required to raise the temperature of a 350 g sample of alcohol from 15$$^\circC to 30$^\circC$$? (Specific heat $$c = 2.47\ \mathrm{J/g}^\circ\mathrm{C})$$

Accepted Answer

$$12,952.5\ \mathrm{J}$$

Question 19

Heated lithium atoms emit photons with an energy of $$2.961 	imes 10$$^{-19}$$\ \mathrm{J}. $$What is the wavelength of one of these photons? ($$c = 3.00 	imes 10^8$\ \mathrm{m/s}$$, $$h = 6.626 	imes 10$$^{-34}$$\ \mathrm{J\cdot s})$$

Accepted Answer

$$6.72 	imes 10$$^{-7}$$\ \mathrm{m}$$

Question 20

What is the geometry of $$\mathrm{CO}_2$$ according to VSEPR theory?

Accepted Answer

Linear

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