Question

myp chemistry unit 1 rehearse

1. use the following data to select two true statements about certain alloys.

gold 19.31g/cm³
silver 10.49g/cm³
copper 8.96g/cm³
alloy 1 16.7g/cm³
alloy 2 10.2g/cm³
a. alloy 1 must contain less gold than silver or copper
b. alloy 1 must contain more gold than silver or copper
c. alloy 2 must contain less silver than gold and copper
d. alloy 2 must contain less gold than silver or copper
e. alloy 1 must contain gold but alloy 2 cannot contain any gold

1. which is not a heterogenous mixture?

a. milk
b. blood
c. wet sand
d. saline (medical salt water)
e. sewage
f. iced tea (with ice)

1. which cannot be broken down by chemical means?

a. water (h₂o)
b. sucrose (c₁₂h₂₂o₁₁)
c. palladium (pd)
d. rust (fe₂o₃)
e. baking soda (nahco₃)

1. which possibly explains why a natural phenomenon occurs?

a. hypothesis
b. conjecture
c. theory
d. educated guess

1. matter that has variable/varying composition is

a. compound
b. element
c. pure substance
d. mixture

1. what is the total number of atoms in 2.0 moles of calcium?

a. 20 atoms
b. 6.02 x 10²³ atoms
c. 40.1 atoms
d. 1.2 x 10²⁴ atoms

1. the amount of substance having 6.022 x 1023 of any kind of particle is called a(n):

a. molecular formula
b. mass number
c. mole
d. molar mass

1. how many moles contain 3.1x10²⁰ molecules of co₂?

a. 0.0051 moles
b. 1.9 e 44 moles
c. 5.1 x 10⁻⁴ moles
d. 0.848 moles

1. how many atoms are contained in 2.4 moles of iron?

a. 4.0 x 10⁻²⁴ atoms
b. 2.4 1x 10²⁴ atoms
c. 1.4 x 10²⁴ atoms
d. 1.44x 10²³ atoms

1. suji wants to test the effect of fertilizer on corn growth. she plants three rows of corn. all of the rows receive the same amount of water and sunlight. she checks the growth of the corn over the course of 5 months. the following table shows the amount of fertilizer placed in each row of corn:

row 1 2 3
fertilizer 0g/m³ 10g/m³ 20g/m³
a. what is a control variable?
i. plant height
ii. amount of fertilizer
iii. amount of water
iv. row 1
b. what is the independent variable?
i. plant height
ii. amount of fertilizer
iii. amount of water
iv. row 1

Explanation:

Step1: Recall mole - Avogadro's number relationship

1 mole of any substance contains $6.022\times 10^{23}$ particles (atoms, molecules, etc.).

Step2: Calculate number of atoms in 2.0 moles of calcium

For 2.0 moles of calcium, we use the formula $N = n\times N_A$, where $n = 2.0$ moles and $N_A=6.022\times 10^{23}$ atoms/mol. So $N=2.0\times6.022\times 10^{23}=1.2044\times 10^{24}\approx1.2\times 10^{24}$ atoms.

Step3: Recall mole definition

The amount of substance having $6.022\times 10^{23}$ of any kind of particle is called a mole.

Step4: Calculate moles of $CO_2$

We know that $n=\frac{N}{N_A}$, where $N = 3.1\times 10^{20}$ molecules of $CO_2$ and $N_A = 6.022\times 10^{23}$ molecules/mol. So $n=\frac{3.1\times 10^{20}}{6.022\times 10^{23}}\approx0.000515\approx0.00051$ moles.

Step5: Calculate number of atoms in 2.4 moles of iron

Using $N = n\times N_A$, with $n = 2.4$ moles and $N_A=6.022\times 10^{23}$ atoms/mol, we get $N=2.4\times6.022\times 10^{23}=1.44528\times 10^{24}\approx1.4\times 10^{24}$ atoms.

Step6: Identify control variable

In an experiment, a control variable is kept constant. Here, the amount of water is kept the same for all rows of corn, so it is a control variable.

Step7: Identify independent variable

The independent variable is the variable that is changed or manipulated. Here, the amount of fertilizer is being changed for different rows of corn, so it is the independent variable.

Answer:

1. d. $1.2\times 10^{24}$ atoms
2. c. mole
3. a. 0.0051 moles
4. c. $1.4\times 10^{24}$ atoms
5. a. iii. Amount of water

b. iii. Amount of fertilizer