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1. Baking soda decomposes at 80 degrees C. How will you determine what happens to washing soda when heated?

2.Write the correctly balanced decomposition reaction for baking soda.

3.If 75 grams of magnesium sulfate heptahydrate is completely dehydrated, how many grams of anhydrous magnesium sulfate will remain? Show your work.

4.If 25 grams of sodium hydrogen carbonate is decomposed to products, how many grams of solid product will remain?

5.In an experiment, 55.0 gramsof solid zinc was reacted with excess copper(II) sulfate solution, producing 41.50 grams of solid copper. Calculate the theoretical yield and the percent yield of copper in this experiment.

Respuesta :

cristisp93

1) You weight the salt before and after the heating.

2) 2 NaHCO₃ → Na₂CO₃ + H₂O + CO₂

3) 36.6 g of anhydrous magnesium sulfate

4) 15.9 g mass of solid  sodium carbonate

5)  yield = 76.47 %

Explanation:

1. We have the following  substances:

baking soda is sodium hydrogen carbonate NaHCO₃

washing soda is sodium carbonate Na₂CO₃

I believe the the questions is asking about baking soda not washing soda, but we will discuss both scenarios.

At 80°C NaHCO₃ (baking soda) is decomposed in sodium carbonate, water and carbon dioxide.

2 NaHCO₃ → Na₂CO₃ + H₂O + CO₂

Sodium carbonate Na₂CO₃ it will crystallize from water as a decahydrate  Na₂CO₃ · 10 H₂O and at 32°C will lose three water molecules to form the heptahydrate Na₂CO₃ · 7 H₂O which at 35°C will lose other six water molecules to form the monohydrate Na₂CO₃ · H₂O.

At 100 °C  the monohydrate salt will lose the remaining water molecule to form the anhydrous sodium carbonate salt. At 851 °C the anhydrous sodium carbonate will melt.

2. To balance the reaction the number and type of atoms entering the reaction have to be equal to the the number and type of atoms leaving the reaction.

2 NaHCO₃ → Na₂CO₃ + H₂O + CO₂

3. The dehydration of magnesium sulfate heptahydrate:

MgSO₄ · 7 H₂O → MgSO₄ + H₂O (g)

number of moles = mass / molecular weight

number of moles of MgSO₄ · 7 H₂O = 75 / 246 = 0.305 moles

0.305 moles of MgSO₄ · 7 H₂O  will form 0.305 moles of anhydrous MgSO₄

mass = number of moles × molecular weight

mass of anhydrous magnesium sulfate = 0.305 × 120 = 36.6 g

4. Decomposition of sodium hydrogen carbonate:

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

number of moles = mass / molecular weight

number of moles of NaHCO₃ = 25 / 84 = 0.3 moles

if        2 moles of NaHCO₃ produces 1 mole of solid Na₂CO₃

then   0.3 moles of NaHCO₃ produces X moles of solid Na₂CO₃

X = (0.3 × 1) / 2 = 0.15 moles of solid Na₂CO₃

mass = number of moles × molecular weight

mass of solid Na₂CO₃ = 0.15 × 106 = 15.9 g

5. Reaction between solid zinc and cooper (II) sulfate:

Zn + CuSO₄ → ZnSO₄ + Cu

number of moles = mass / molecular weight

number of moles of Zn = 55 / 65 = 0.85 moles

number of moles of Cu = 41.5 / 63.5 = 0.65 moles

From the reaction we see that 1 mole of zinc will produce 1 mole of cooper. Theoretical yield is the one in which all the zinc quantity, 0.85 moles,   reacted and is 100%.

Percent yield is the practical yield and is calculated taking in account the actual quantity of zinc that have been reaction.

We see that the reaction produced 0.65 moles of cooper that means then only 0.65 moles of Zn reaction from the entire quantity of 0.85 moles.

yield = (practical quantity / theoretical quantity) × 100

yield = (0.65 / 0.85) × 100 = 76.47 %

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