Question

1. How many hydrogen atoms are in 5 molecules of isopropyl alcohol, C3H7O

Answer 1

1. c. 35
2. d. 1.26 x 10^24 molecules 
3. d. 303.6 g 

Answer 2

These are three questions and three answers.

Question 1. How many hydrogen atoms are in 5 molecules of isopropyl alcohol, C₃H₇O

Answer: option c. 35

Justification:

The unit formula C₃H₇O corresponds to one molecule of isopropylalcohol.

The capitalized letters are the chemical symbols of the different elements or type of atoms. So, C is for carbon, H is for hydrogen, and O is for oxygen.

The subscripts to the right of each chemical symbol indicate the number of atoms for the corresponding element in the unit formula.

So, C₃ means that there are 3 atoms of carbon in one molecule of isopropyl alcohol; H₇ means that there are 7 atoms of hydrogen in one molecule of isopropyl alcohol; and in O it is understood that the subscript is one, meaning that there is 1 atom of oxygen in one molecule of isopropyl alcohol.

Since, there are 5 molecules of isopropyl alcohol, the number of each kind of atom is five times the respective subscripts.

For the hydrogen, it means that there are 5 × 7 = 35 atoms of hydrogen in 5 molecules of isopropyl alcohol, C₃H₇O.

Question 2. How many molecules are in 2.10 mol CO2?

Answer: option d., 1.26 x 10²⁴ molecules

Explanation:

The mole is the basic SI unit to measure the amount of a substance. One mole is equal to 6.022×10²³ particles. So, 1 mole of molecules is 6.022×10²³ molecules.

Hence, to find how many molecules are in 2.10 mol of CO₂ you just multiply 2.10 times 6.022×10²³ :

• 2.10 × 6.022×10²³ = 12.65×10²³ ≈ 1.26×10²⁴

S0. the answer is the option d.

Quesiton 3. What is the molar mass of AuCl3?

Answer: option d., 303.6 g

Explanation;

The molar mass is the mass of one mole of substance.

In this case the unit formula of the substance is AuCl₃.

Then, since one uni formula has one atom of Au and three atoms of Cl, you must add the mass of the four atoms to obtain the molar mass.

The masses of the atoms (atomis masses) are reported in the periodic table. Here is how you do the calculations:

Element          atomic mass (g/mol) ×  number of atoms =  total mass

Au                    196.967 g/mol                 1                             196.967 g/mol

Cl                       35.453 g/mol                3                            106.359 g/mol

                                                                       sum                 303.326 g/mol

Hence, the answer is the molar mass of AuCl₃ is given by the option d. 303.6 g/mol