1. A chemist prepares hydrogen fluoride by means of the following reaction:
CaF2 + H2SO4 -> CaSO4 + 2HF
The chemist uses 11 g of CaFz and an excess of H2SO4, and the reaction produces 2.2 g of HF.
(a) Calculate the theoretical yield of HF.
(b) Calculate the percent yield of HF.

a) Theoretical Yield of HF = 5.64 grams

b) Percentage Yield = 39%

Explanation:

Reaction Given:

CaF2 + H2SO4 -> CaSO4 + 2HF

CaF2 = 11g

H2SO4 = Used in excess

HF = 2.2 g production = Actual Yield

So, Let's write down the molar masses:

Molar Mass of CaF2 = 78 g /mol

Molar Mass of HF = 20 g/mol

From the reaction, we can see the 1 mole of CaF2 gives the 2 moles of HF

i.e

a) Theoretical Yield of HF:

1 mole CaF2 = 2 moles HF

78 g CaF2 = 2 x 20 g of HF

78 g CaF2 = 40 g of HF

1 g CaF2 = 40g/78g of HF

And in the question it is given that chemist used 11 g of CaF2 so,

1 x 11 g of CaF2 = 11 x 40/78 g of HF

11 g of CaF2 = 440/78 g of HF

11 g of CaF2 = 5.64 g of HF

And this is the theoretical yield

Theoretical Yield of HF = 5.64 grams

b) Now, calculate the Percentage Yield of HF

Percentage Yield = Actual Yield /Theoretical Yield x 100

Percentage Yield = 2.2 g /5.64 g x 100

Percentage Yield = 39%

gas

explanation:

hdahhd

              nitroswawdasdwasdawsdwasdwasdwasdwaswasdwasdawdswasdwadwadswadadadasd gay

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.