Question

1. what is the formula for diphosphorus pentachloride?

a. p₂cl₄ c. pcl₅
b. p₂cl₅ d. p₅cl₂

1. what is the percent composition of each element in copper ii chloride?

a. 33% cu, 66% cl
b. 50% cu, 50% cl
c. 65.50% cu, 34.50% cl
d. 47.26% cu, 52.74% cl

1. a lab procedure instructs you to obtain 5.0 grams of a substance, and your balance reads 6.3 grams of the substance. what should you do?

a. ask your teacher how to dispose of the extra.
b. put the extra back into the original container.
c. use the extra amount because it won’t matter to the lab.
d. throw the extra into the garbage.

1. what is the mass of 2.6 x 10²³ molecules of h₂so₄?

a. 42. grams h₂so₄
b. 1.5 x 10⁴⁹ grams h₂so₄
c. 0.43 grams h₂so₄
d. 5.9 x 10²⁵ grams h₂so₄
e. 1.6 x 10⁴⁵ grams h₂so₄

1. which of the following descriptions of a subatomic particle is correct?

a. a proton has a positive charge and a mass of approximately 1 amu.
b. an electron has a negative charge and a mass of approximately 1 amu.
c. a neutron has no charge and its mass is negligible (about 0 amu).
d. a proton has a positive charge and a negligible mass (about 0 amu).

1. elements in a group or column in the periodic table can be expected to have similar...

a. atomic masses. c. number of neutrons.
b. atomic numbers. d. chemical and physical properties.

1. what would be the mass of 3,720 atoms of au?

a. (3,720 atoms au / 1) x (6.022 x 10²³ atoms au / 1 mol au) x (1 mol au / 196.9665 g au) = 1.14 x 10²⁵ mol au
b. (3,720 atoms au / 1) x (1 mol au / 6.022 x 10²³ atoms au) x (196.9665 g au / 1 mol au) = 1.21 x 10⁻¹⁸ g au
c. (3,720 atoms au / 1) x (1 mol au / 6.022 x 10²³ atoms au) x (196.9665 g au / 1 mol au) = 1.21 x 10²⁸ g au
d. (3,720 atoms au / 1) x (196.9665 g au / 1 atom au) = 7.33 x 10⁵ g au

Explanation:

Step1: Name to formula

Diphosphorus = $P_2$, pentachloride = $Cl_5$, so formula is $P_2Cl_5$.

Step2: Find molar mass of $CuCl_2$

Molar mass $= 63.55 + 2\times35.45 = 134.45$ g/mol.
% Cu = $\frac{63.55}{134.45} \times100\% \approx47.26\%$, % Cl = $100\%-47.26\%=52.74\%$.

Step3: Lab safety protocol

Never return excess chemicals to stock containers, do not discard in regular trash, follow teacher instructions for disposal.

Step4: Calculate mass of $H_2SO_4$

Moles = $\frac{2.6\times10^{23}}{6.022\times10^{23}} \approx0.432$ mol. Molar mass $H_2SO_4=98.08$ g/mol. Mass = $0.432\times98.08\approx42$ g.

Step5: Subatomic particle properties

Proton mass ≈1 amu, positive charge; electron mass ≈0 amu, negative charge; neutron mass≈1 amu, neutral.

Step6: Periodic table group properties

Groups share valence electrons, so similar chemical/physical properties.

Step7: Convert atoms Au to mass

Use dimensional analysis: $\frac{3720}{6.022\times10^{23}} \times196.9665 \approx1.21\times10^{-18}$ g Au.

Answer:

1. 41. b. $P_2Cl_5$
2. 42. d. 47.26% Cu, 52.74% Cl
3. 43. a. Ask your teacher how to dispose of the extra.
4. 44. a. 42. grams $H_2SO_4$
5. 45. a. A proton has a positive charge and a mass of approximately 1 amu.
6. 46. d. chemical and physical properties.
7. 47. b. $\frac{3,720 \text{ atoms Au}}{1} \times \frac{1 \text{ mol Au}}{6.022 \times 10^{23} \text{ atoms Au}} \times \frac{196.9665 \text{ g Au}}{1 \text{ mol Au}} = 1.21 \times 10^{-18} \text{ g Au}$