Can someone please help with these questions I’ve been stuck on them all day and literally don’t know what to do!?

(1) Here you first calculate the amount of substance from the mass and the molar mass. Then you multiply by the constant.

first: n = m / M             then: n * 6 * 10²³ = number of atoms

a) n = 4 g / 24 g/mol            number of atoms = 0,166 mol * 6 * 10²³ 1/mol

   n = 0,166 mol                   number of atoms = 0,96 * 10²³

b) n = 0,12 g / 12 g/mol       number of atoms = 0,01 mol * 6 * 10²³ 1/mol

   n = 0,01 mol                    number of atoms = 0,06 * 10²³

c) n = 32 g /48 g/mol         number of molecules = 0,666 mol * 6 * 10²³ 1/mol

   n = 0,666 mol                number of molecules = 4 * 10²³

d) n = 14,2 g / 71 g/mol      number of molecules = 0,2 mol * 6 * 10²³ 1/mol

   n = 0,2 mol                     number of molecules = 1,2 * 10²³

   Sodium sulfate has the formula Na2SO4, so it has two sodium atoms per  

   molecule. So you have to multiply the number of molecules by 2.

   number of atoms = number of molecules * 2

   number of atoms = 1,2 * 10²³ * 2

   number of atoms = 2,4 * 10²³

(2) The amount of substance can easily be calculated:

n = m / M

a) n = 16 g / 16 g/mol

   n = 1 mol

b) n = 0,14 g / 14 g/mol

   n = 0,01 mol

c) n = 5,4 g / 108 g/mol

   n = 0,05 mol

d) n = 8,88 g / 35,5 g/mol

   n = 0,25 mol

(3) With the same formula the mass can now be calculated, for this it only has to be converted according to the mass:

n = m / M      | *M

m = n * M

a) m = 0,05 mol * 16 g/mol

   m = 0,8 g

b) m = 10 mol * 23 g/mol

   m = 230 g

c) m = 0,01 mol * 1 g/mol

   m = 0,01 g

d) m = 0,25 mol * 65,4 g/mol

   m = 16,35 g

(4) The molar mass of a molecule is obtained by adding the molar masses of the individual atoms:

a) Br = 80 g/mol → Br2 = 2 * 80 g/mol = 160 g/mol

b) C = 12 g/mol, O = 16 g/mol → CO2 = 12 g/mol + 2 * 16 g/mol = 44 g/mol

c) H = 1 g/mol, N = 14 g/mol, O = 16 g/mol

  → HNO3 = 1 g/mol + 14 g/mol + 3* 16 g/mol = 63 g/mol

d) Cu = 64 g/mol, S = 32 g/mol, O = 16 g/mol,  H = 1 g/mol

   →CuSO4*5H2O = 64 g/mol + 32 g/mol + 4 * 16 g/mol + 5 * (2 * 1 g/mol +

     16 g/mol) = 250 g/mol

(5) Exercise 5 works exactly like exercise 2 and 4:

first: Calculate molar mass                    then: n = m / M

a) n = 128 g / 16 g/mol

   n = 8 mol

b) M = 39 g/mol + 14 g/mol + 3 * 16 g/mol

   M = 101 g/mol

   n = 25,25 g / 101 g/mol

   n = 0,25 mol

c) M = 2 * 12 g/mol + 6 * 1 g/mol + 16 g/mol

   M = 46 g/mol

   n = 414 g / 46 g/mol

   n = 9 mol

(6) Exercise 6 works exactly the same as exercises 3 and 4:

first: Calculate molar mass                    then: m = n * M

a) M = 32 g/mol + 2 * 16 g/mol

   M = 64 g/mol

   m = 2 mol * 64 g/mol

   m = 128 g

b) M = 2 * 1 g/mol + 32 g/mol + 4 * 16 g/mol

   M = 98 g/mol

   m = 20 mol * 98 g/mol

   m = 1960 g

c) M = 23 g/mol + 16 g/mol + 1 g/mol

   M = 40 g/mol

   m = 0,5 mol * 40 g/mol

   m = 20 g

hey there!

mass = 6.75 g

volume =   9 cm³

therefore:

d = mass / volume

d   = 6.75 / 9

d = 0.7 g/cm³

answer b