Question

unit 1- matter and the mole

1. which substance cannot be decomposed into simpler substances?

a. ammonia b. aluminum c. methane d. methanol

1. a compound differs from a mixture in that a compound always has a

a. homogeneous composition b. maximum of two components c. minimum of three components d. heterogeneous composition

1. an experiment for a new asthma medication was set up into two groups. group one was given the new drug for asthma, while group 2 was given a sugar pill. the sugar pill serves as

a. control b. constant c. experimental variable d. dependent variable

1. to determine the density of an irregularly - shaped object, a student immersed the object in 21.2 milliliters of h₂o in a graduated cylinder, causing the level of the h₂o to rise to 27.8 milliliters. if the object had a mass of 22.4 grams, what was the density of the object.

a. 27.8 g/ml b. 6.6 g/ml c. 3.0 g/ml d. 3.4 g/ml
use the following scenario to answer questions26 and 27. a scientist plants two rows of corn for experimentation. she puts fertilizer on row 1 but does not put fertilizer on row 2. both rows receive the same amount of water and light intensity. she checks the growth of the corn over the course of 5 months.

1. what is a constant in this experiment?

a. plant height b. corn without fertilizer c. amount of water

1. what is the independent variable in this experiment?

a. plant height b. corn without fertilizer c. amount of water

1. the measurable factor in an experiment is known as the:

a. control b. independent variable c. constant d. dependent variable

1. how many moles of sodium are 6.02×10²³ atoms of sodium?

a. 0.5 b. 1.0 c. 1.5 d. 2

1. how many molecules are in 1 mole of water?

a. 3 b. 54 c. 6.02×10²³ d. 2(6.02×10²³) e. 3(6.02×10²³)

1. how many atoms are represented in the formula ca₃(po₄)₂

a. 5 b. 8 c. 9 d. 12 e. 13

1. what is the total number of atoms contained in 2.00 moles of nickel?

a. 58.9 b. 118 c. 6.02×10²³ d. 1.2×10²⁴

1. the amount of substance having 6.022×10²³ of any kind of chemical unit is called a(n):

a. formula b. mass number c. mole d. atomic weight

1. the total number of atoms in a formula unit of aluminum dichromate, al₂(cr₂o₇)₃ is:

a. 5 b. 29 c. 17 d. 11

Explanation:

Step1: Define element

Elements cannot be decomposed into simpler substances. Aluminum is an element, while ammonia ($NH_3$), methane ($CH_4$), and methanol ($CH_3OH$) are compounds.

Step2: Define compound and mixture

A compound has a homogeneous composition. A mixture can be homogeneous or heterogeneous and has no fixed - ratio of components.

Step3: Define control in experiment

In an experiment, the control group is not exposed to the experimental variable. The sugar pill in the asthma - medication experiment serves as the control.

Step4: Calculate volume of object

The volume of the object is the change in water level in the graduated cylinder. $V=27.8\ mL - 21.2\ mL=6.6\ mL$.

Step5: Calculate density

Density $
ho=\frac{m}{V}$, where $m = 22.4\ g$ and $V = 6.6\ mL$. So $
ho=\frac{22.4\ g}{6.6\ mL}\approx3.4\ g/mL$.

Step6: Define constant in experiment

Constants are factors that are kept the same in an experiment. The amount of water is a constant in the corn - growth experiment.

Step7: Define independent variable

The independent variable is the factor that is changed or manipulated in an experiment. Fertilizer (presence or absence) is the independent variable in the corn - growth experiment.

Step8: Define dependent variable

The measurable factor in an experiment is the dependent variable.

Step9: Use Avogadro's number

Avogadro's number $N_A = 6.02\times10^{23}\ mol^{-1}$. The number of moles $n=\frac{N}{N_A}$. For $N = 6.02\times10^{23}$ sodium atoms, $n=\frac{6.02\times10^{23}}{6.02\times10^{23}\ mol^{-1}} = 1.0\ mol$.

Step10: Recall Avogadro's number for molecules

1 mole of any substance contains $6.02\times10^{23}$ molecules. So 1 mole of water contains $6.02\times10^{23}$ water molecules.

Step11: Count atoms in formula

In $Ca_3(PO_4)_2$, there are 3 Ca atoms, 2 P atoms, and 8 O atoms, for a total of 13 atoms.

Step12: Calculate number of atoms

Using $N=nN_A$, for $n = 2.00\ mol$ of nickel, $N=2.00\ mol\times6.02\times10^{23}\ mol^{-1}=1.2\times10^{24}$ atoms.

Step13: Define mole

The amount of substance having $6.022\times10^{23}$ of any kind of chemical unit is called a mole.

Step14: Count atoms in formula unit

In $Al_2(Cr_2O_7)_3$, there are 2 Al atoms, 6 Cr atoms, and 21 O atoms, for a total of 29 atoms.

Answer:

1. b. aluminum
2. a. homogeneous composition
3. a. Control
4. d. 3.4 g/mL
5. c. Amount of water
6. b. Corn without fertilizer
7. d. dependent variable
8. b. 1.0
9. c. $6.02\times10^{23}$
10. e. 13
11. d. $1.2\times10^{24}$
12. c. mole
13. b. 29