Pre-test Cy Quiz

What is the number of hydrogen atoms in 39.6 g of ammonium sulphate, (NH4)2SO4?

• 3.78 x 10^22

• 5.91 x 10^21

• 2.56 x 10^23

• 1.44 x 10^24

Answer explanation

1. Calculate the molar mass of (NH4)2SO4.

2. Convert the given mass of ammonium sulfate (39.6 g) to moles.

3. Use the mole ratio between (NH4)2SO4 and hydrogen atoms to find the number of moles of hydrogen.

4. Convert the moles of hydrogen to atoms.

Let's begin:

1. The molar mass of (NH4)2SO4 can be calculated as follows: Molar mass of NH4 = 14.01 (molar mass of nitrogen) + 4(1.008) (molar mass of hydrogen) = 14.01 + 4.032 = 18.042 g/mol Molar mass of SO4 = 32.07 (molar mass of sulfur) + 4(16.00) (molar mass of oxygen) = 32.07 + 64.00 = 96.07 g/mol Molar mass of (NH4)2SO4 = 2(18.042) + 96.07 = 36.084 + 96.07 = 132.154 g/mol

2. Now, let's convert the given mass of ammonium sulfate to moles: Number of moles = Mass / Molar mass = 39.6 g / 132.154 g/mol ≈ 0.2995 moles

3. From the formula (NH4)2SO4, we can see that there are 8 hydrogen atoms for every mole of (NH4)2SO4.

4. So, the number of hydrogen atoms = 8 * 0.2995 ≈ 2.396

Since we have calculated the number of hydrogen atoms in moles, we need to convert this to atoms by multiplying by Avogadro's number:

2.396×6.022×10232.396×6.022×1023

This calculation gives us approximately 1.44×10241.44×1024.

So, the correct answer is 1.44 x 10^24.

What is the empirical formula of a compound composed of 52.14% carbon, 13.13% hydrogen, and 34.73% oxygen by mass?

• C2H6O

• C6H18O3

• C3H8O2

• C4H10O3

Answer explanation

1. Convert the percentages to grams. Assume we have 100 grams of the compound, so we'll have 52.14 g of carbon, 13.13 g of hydrogen, and 34.73 g of oxygen.

2. Convert the masses of each element to moles using their respective molar masses:

   • Carbon (C): 52.14 g / 12.01 g/mol ≈ 4.34 moles

   • Hydrogen (H): 13.13 g / 1.008 g/mol ≈ 13.02 moles

   • Oxygen (O): 34.73 g / 16.00 g/mol ≈ 2.17 moles

3. Divide each number of moles by the smallest number of moles to find the simplest whole-number ratio. In this case, oxygen has the smallest number of moles, so we divide all moles by 2.17:

   • Carbon: 4.34 moles / 2.17 ≈ 2

   • Hydrogen: 13.02 moles / 2.17 ≈ 6

   • Oxygen: 2.17 moles / 2.17 = 1

4. The simplest whole-number ratio of atoms is approximately C2H6O.

What is the molar mass of Ca(NO3)2?

• 164.09 g/mol

• 164.10 g/mol

• 164.11 g/mol

• 164.12 g/mol

Balance the equation: C3H8 + O2 -> CO2 + H2O

• C3H8 + 5 O2 -> 3 CO2 + 4 H2O

• C3H8 + 5 O2 -> 3 CO2 + 4 H2O

• C3H8 + 5 O2 -> 3 CO2 + 5 H2O

• C3H8 + 4 O2 -> 3 CO2 + 5 H2O

What is the oxidation state of sulfur in H2SO4?

• +2

• +4

• +6

• +8

Answer explanation

In H2SO4 (sulfuric acid), sulfur can have different oxidation states. Let's calculate it:

Let's assign "x" as the oxidation state of sulfur.

The oxidation state of hydrogen (H) is +1 in most compounds, and the oxidation state of oxygen (O) is typically -2.

In H2SO4, we have:

(2×(+1))+ X +4(−2)=0(2×(+1))+x+4(−2)=0

2+ X − 8=02+x−8=0

X −6=0x−6=0

X =+6x=+6

So, the oxidation state of sulfur in H2SO4 is +6.

Therefore, the correct answer is +6.

Balance the equation: H2 + O2 -> H2O

• 2 H2 + O2 -> 2 H2O

• H2 + O2 -> H2O

• 2 H2 + 2 O2 -> 2 H2O

• H2 + 2 O2 -> H2O

What is the oxidation state of nitrogen in NH3?

• -1

• +1

• -3

• +3

What is the molar mass of NaCl?

• 58.44 g/mol

• 58.45 g/mol

• 58.46 g/mol

• 58.47 g/mol

How many significant figures are in the number 0.00345.

• 2

• 3

• 4

• 5

Answer explanation

Significant figures are the digits of a number that are meaningful in terms of accuracy or precision.

They include:

• Any non-zero digit

• Zeros between non-zero digits as in 3003 or 45.60009

• Trailing zeros only when there is a decimal point as in 6750. or 274.3300.

How to Identify Non-Significant Figures.

They include:

• Leading zeros as in 0.009 or 0056

• Trailing zeros as in 45000 when no decimal point is present.

2. How many significant figures are in the number 9000?

• 1

• 2

• 4

Answer explanation

1. Non-zero digits are always significant

2. Zeros between non-zero digits are always significant

3. Leading zeros are never significant

4. Trailing zeros are only significant if the number contains a decimal point