Question

Sodium bicarbonate (
`NaHCO_3`) decomposes upon heating above 500 K as shown in the unbalanced chemical equation below. On the other hand, sodium

carbonate (
`Na_2CO_3`) does NOT decompose upon heating.


`NaHCO_3_(_s_) -(heat)-\ \textgreater \ Na_2CO_3_(_s_)+CO_2_(_g_)+H_2O_(_g_)`

A student is given 14.00 g of a mixture containing both sodium carbonate and sodium bicarbonate in a small plastic vial. After heating to the point where all the sodium bicarbonate is decomposed there is a mass loss of 2.28 g.
Answer all parts of the question below.

1. Write a balanced equation for the decomposition of sodium bicarbonate by heating.

2. Describe the process by which you would heat the mixture and determine the mass loss.

3. Indicate how you would know that all the sodium bicarbonate had been decomposed.

4. Determine the % of
`Na_2CO_3` that was contained in the original mixture.

5. Is the sodium bicarbonate or the sodium carbonate the limiting reactant? Explain your reasoning.

Answer 1

1. Balanced equation for the decomposition of sodium bicarbonate by heating:

2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g)

2. To heat the mixture and determine the mass loss, the following process can be used:

- Weigh the vial with the mixture to obtain the initial mass.

- Heat the vial to a temperature above 500 K until no more mass loss is observed.

- Weigh the vial with the remaining mixture to obtain the final mass.

- Calculate the mass loss by subtracting the final mass from the initial mass.

- The mass loss will be equal to the mass of the CO2 and H2O produced during the decomposition of the NaHCO3.

3. All the sodium bicarbonate has been decomposed when the mass loss stops, which means that no more CO2 and H2O are being produced. This can be confirmed by checking the mass of the vial and mixture after heating and ensuring that it is constant.

4. To determine the % of Na2CO3 that was contained in the original mixture:

- Calculate the mass of NaHCO3 that decomposed by subtracting the mass loss from the initial mass of the mixture.

- Convert the mass of NaHCO3 to moles by dividing by the molar mass of NaHCO3 (84.01 g/mol).

- Use the balanced equation to find the number of moles of Na2CO3 produced.

- Convert the moles of Na2CO3 to grams by multiplying by the molar mass of Na2CO3 (105.99 g/mol).

- Calculate the % of Na2CO3 in the original mixture by dividing the mass of Na2CO3 produced by the initial mass of the mixture and multiplying by 100.

5. The sodium bicarbonate is the limiting reactant because it is the only reactant that decomposes during heating. The mass loss observed during the experiment is directly related to the amount of NaHCO3 that decomposed. Therefore, the amount of Na2CO3 in the original mixture is irrelevant to determining the limiting reactant.

Step-by-step explanation:

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Answer 2

1. The balanced equation for the decomposition of sodium bicarbonate by heating is 2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(l). 2. To determine the mass loss, you would heat the mixture and measure the initial and final mass of the vial. 3. When there is no longer any mass loss upon further heating, it indicates that all the sodium bicarbonate has been decomposed. 4. To calculate the % of Na2CO3 in the original mixture, divide the mass loss by the initial mass and multiply by 100%. 5. The limiting reactant is the one that is completely consumed and determines the amount of product that can be formed.

Step-by-step explanation:

1. The balanced equation for the decomposition of sodium bicarbonate by heating is:

2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(l)

2. To determine the mass loss, you would heat the mixture in a small plastic vial until all the sodium bicarbonate is decomposed. Then, you would measure the initial and final mass of the vial and subtract the final mass from the initial mass to calculate the mass loss.

3. You would know that all the sodium bicarbonate has been decomposed when there is no longer any mass loss upon further heating. In other words, the mass of the vial remains constant.

4. To determine the % of Na2CO3 in the original mixture, you would use the mass loss of 2.28 g and the initial mass of the mixture. Calculate the % by dividing the mass loss by the initial mass and multiplying by 100%.

5. To determine the limiting reactant, you would compare the moles of NaHCO3 and Na2CO3 in the mixture. Whichever reactant has the smaller amount of moles is the limiting reactant. The limiting reactant is the one that is completely consumed and determines the amount of product that can be formed.