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3 years ago

How many grams of oxygen (O) are present in 0.0207 moles of Ca(HCO 3) 2

Chemistry

1 answer:

Zolol [24]3 years ago

5 0

Answer:

1.99grams

Explanation:

- First, we need to calculate the molar mass of the compound: Ca(HCO3)2

Ca = 40g/mol, H = 1g/mol, C = 12g/mol, O = 16g/mol

Hence, Ca(HCO3)2

= 40 + {1 + 12 + 16(3)}2

= 40 + {13 + 48}2

= 40 + {61}2

= 40 + 122

= 162g/mol

Molar mass of Ca(HCO3)2 = 162g/mol

- Next, we calculate the mass of oxygen in one mole of the compound, Ca(HCO3)2.

Oxygen = {16(3)}2

= 48 × 2

= 96g of Oxygen

- Next, we calculate the percentage composition of oxygen by mass by dividing the mass of oxygen in the compound by the molar mass of the compound i.e.

% composition of O = 96/162 × 100

= 0.5926 × 100

= 59.26%.

- The number of moles of the compound, Ca(HCO3)2, must be converted to mass by using the formula; mole = mass/molar mass

0.0207 = mass/162

Mass = 162 × 0.0207

Mass = 3.353grams

However, in every gram of Ca(HCO3)2, there is 0.5926 g of oxygen

Hence, in 3.353grams of Ca(HCO3)2, there will be;

0.5926 × 3.353

= 1.986

= 1.99grams.

Therefore, there is 1.99grams of Oxygen in 0.0207 moles (3.353g) of Ca(HCO3)2.

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The active ingredient in aspirin is acetylsalicylic acid. A 2.79 g sample of acetylsalicylic acid required 30.15 mL of 0.5137 M

vivado [14]

Answer:

Molar mass = 180 g/mol

Ka = 3.31x10⁻⁴

Explanation:

Because the acetylsalicylic is a monoprotic acid, it only leaves 1 mol of H⁺ in the reaction, so, it's necessary 1 mol of NaOH for each 1 mol of acetylsalicylic acid. The number of moles of NaOH is the volume, in L, multiplied by the concentration:

n = 0.03015*0.5137 = 0.01549

Which is also the number of moles of the acid. The molar mass is the mass, in g, divided by the number of moles:

M = 2.79/0.01549

M = 180 g/mol

After reacting with the base, the conjugate base of the acid will be formed, and the equilibrium between the acid form (HA) and the conjugate base (A⁻) is a buffer. It formed 0.01549 moles of A⁻, which will react with the moles of H⁺ from HCl to form HA.

nH⁺ = nHCl = 0.01741*0.448 = 0.0078 mol

A⁻ + H⁺ ⇄ HA

0.01549 0.0078 0 Initial

-0.0078 -0.0078 +0.0078 Reacts

0.0078 0 0.0078 Equilibrium

For a buffer, the pH can be calculated by the Handerson-Halsebach equation:

pH = pKa + log[A⁻]/[HA]

Because the volume is the same, we can use the number of moles instead of the concentration:

3.48 = pKa + log(0.0078/0.0078)

pKa = 3.48

pKa = -logKa

Ka = $10^{-pKa}$