If a student attempts to identify an unknown compound by methodused in this experiment. She finds that when she heated a sampleweighing 0.4862 g the mass went down appreciably, to 0.3067 g. Whenthe product was converted to chloride, the mass went up, to 0.3382g.
a. Is the sample a carbonate? Give yourreasoning.
b. What are the two compounds that might be theunknown?
c. Write the chemical equation for the overallreaction that would occur when the original compound was convertedto a chloride. If the compound is a hydrogen carbonate, use the sumof Reactions 1 and 2. If the sample is carbonate, use Reaction 2.Write the equation for a sodium salt and the for a potassiumsalt.
d. How many moles of the chloride salt would beproduce from one mole of the original compound?
e. How many grams of the chloride salt would beproduced from one molar mass of the original compound?
Molar masses: NaHCO3 _______g Na2CO3 _______g NaCl_______g
KHCO3 _______g K2CO3 _______g KCl_______g
If a sodium salt, _______g original compound -> _______g chloride
If a potassium salt, _______g original compound -> _______gchloride
f. What is the theoretical mass ratio, mass chloride/mass original compoud?
If she has an Na salt _______:1 if she has a K salt _______:1
g. What was the observed mass ratio,mass chloride/mass original salt?
h. Which compound did she have an unknown?
a. Well, if the mass went down when heated and then went up when converted to chloride, it suggests that the original compound contained an anion that got kicked out when heated and then replaced with a chloride ion. Carbonates are known to do that, so it's a possibility.
b. The two compounds that might be the unknown are sodium carbonate (Na2CO3) and potassium carbonate (K2CO3).
c. The chemical equation for the overall reaction when the original compound is converted to a chloride depends on whether the compound is a hydrogen carbonate or a carbonate:
- If the compound is a hydrogen carbonate (NaHCO3 or KHCO3), the equation would be: NaHCO3 (or KHCO3) + HCl → CO2 + H2O + NaCl (or KCl)
- If the compound is a carbonate (Na2CO3 or K2CO3), the equation would be: Na2CO3 (or K2CO3) + 2HCl → CO2 + H2O + 2NaCl (or 2KCl)
d. From the balanced equations above, we can see that one mole of the original compound would produce two moles of the chloride salt.
e. To find the gram ratio, we need the molar masses of the compounds:
- NaHCO3: _______g
- Na2CO3: _______g
- NaCl: _______g
- KHCO3: _______g
- K2CO3: _______g
- KCl: _______g
If it's a sodium salt:
- _______g of the original compound -> _______g of chloride
If it's a potassium salt:
- _______g of the original compound -> _______g of chloride
f. The theoretical mass ratio would depend on the molar masses of the compounds and the balanced equations. Unfortunately, the molar masses of the compounds are missing, so we can't calculate the exact ratios.
g. The observed mass ratio, mass chloride/mass original salt, is not given in the question. Maybe they left it out to add suspense?
h. As the information provided is not sufficient for a definitive answer, we can't determine which compound she had as an unknown. It remains a mystery, just like the missing observed mass ratio.
To answer this question, let's break it down step by step:
a. To determine if the sample is a carbonate, we need to analyze the mass changes during the experiment. When the sample is heated, the mass decreases, indicating the loss of a volatile component. This suggests that the sample may contain a carbonate, as carbonates release carbon dioxide gas upon heating.
b. Based on the information given, there are two possible compounds that could be the unknown: sodium carbonate (Na2CO3) and potassium carbonate (K2CO3).
c. The chemical equation for the conversion of the original compound to a chloride is as follows:
Na2CO3 + 2HCl -> 2NaCl + H2O + CO2 (for sodium carbonate)
K2CO3 + 2HCl -> 2KCl + H2O + CO2 (for potassium carbonate)
d. From the balanced equation, we can see that 1 mole of the original compound will produce 2 moles of the chloride salt.
e. To find the mass of the chloride salt produced from one molar mass of the original compound, we need to calculate the molar mass of the original compound.
The molar masses are:
NaHCO3: 84.01 g/mol
Na2CO3: 105.99 g/mol
NaCl: 58.44 g/mol
KHCO3: 100.12 g/mol
K2CO3: 138.21 g/mol
KCl: 74.55 g/mol
If the original compound is a sodium salt:
(105.99 g Na2CO3 / 1 mol Na2CO3) x (2 mol NaCl / 1 mol Na2CO3) x (58.44 g NaCl / 1 mol NaCl) = _______ g chloride
If the original compound is a potassium salt:
(138.21 g K2CO3 / 1 mol K2CO3) x (2 mol KCl / 1 mol K2CO3) x (74.55 g KCl / 1 mol KCl) = _______ g chloride
f. To find the theoretical mass ratio of chloride to the original compound, we need to use the molar masses calculated in the previous step.
If she has an Na salt: (_______ g chloride) / (_______ g original compound) = _______:1
If she has a K salt: (_______ g chloride) / (_______ g original compound) = _______:1
g. The observed mass ratio of chloride to the original salt can be calculated using the masses given in the problem:
(0.3382 g chloride) / (0.4862 g original compound) = _______:1
h. Based on the observed mass ratio, compare it to the theoretical mass ratios calculated in step f to determine which compound she had as an unknown. The compound with the matching mass ratio is the unknown compound she had.
Note: Please fill in the blanks with the values obtained from the calculations and molar masses provided.
To answer these questions, we need to analyze the mass changes and perform some calculations based on the given information.
a. To determine if the sample is a carbonate, we compare the change in mass when heated. Carbonates usually decompose when heated, producing carbon dioxide gas (CO2) and a metal oxide. If the mass decreases significantly, it indicates the presence of a carbonate.
Here's how you can calculate the change in mass:
Original mass - Final mass = Change in mass
0.4862 g - 0.3067 g = 0.1795 g
Since the mass decreased appreciably, it suggests the presence of a carbonate compound.
b. We have two possible compounds that could be the unknown: sodium carbonate (Na2CO3) and potassium carbonate (K2CO3). These are common carbonates that can be converted into chloride salts.
c. The chemical equation for the overall reaction depends on whether we have a hydrogen carbonate (bicarbonate) or carbonate. Let's consider both scenarios:
If the compound is a hydrogen carbonate (NaHCO3 or KHCO3), the reaction involves two steps:
Reaction 1: Hydrogen carbonate decomposes to form carbon dioxide gas, water, and a metal oxide.
NaHCO3 → Na2O + CO2 + H2O
KHCO3 → K2O + CO2 + H2O
Reaction 2: The resulting oxide reacts with hydrochloric acid (HCl) to form the chloride salt.
Na2O + 2HCl → 2NaCl + H2O
K2O + 2HCl → 2KCl + H2O
If the sample is a carbonate (Na2CO3 or K2CO3), we only need Reaction 2:
Na2CO3 + 2HCl → 2NaCl + CO2 + H2O
K2CO3 + 2HCl → 2KCl + CO2 + H2O
d. To determine the mole ratio of the chloride salt produced from one mole of the original compound, we need to calculate the moles of each compound. Using the molar masses provided, calculate the moles of the original compound and the moles of the chloride salt.
Moles of original compound = Mass of original compound / Molar mass of original compound
e. To calculate the grams of the chloride salt produced from one molar mass of the original compound, we need to know the molar mass of the chloride salt. Let's calculate the moles of the original compound using the previous calculation, and then convert the moles to grams using the molar mass of the chloride salt.
Grams of chloride salt = Moles of original compound * Molar mass of chloride salt
f. The theoretical mass ratio, which is the ratio of mass chloride to mass original compound, can be calculated using the molar masses of the compounds.
If the sample is an Na salt:
Theoretical mass ratio = Molar mass of NaCl / Molar mass of original compound
If the sample is a K salt:
Theoretical mass ratio = Molar mass of KCl / Molar mass of original compound
g. The observed mass ratio is determined by dividing the mass of the chloride salt by the mass of the original compound, as mentioned in the question. This value needs to be compared with the theoretical mass ratio calculated in step f.
h. Based on the observed mass ratio and the theoretical mass ratios for both sodium and potassium salts, we can determine which compound the student had as the unknown. If the observed mass ratio matches the theoretical mass ratio for either sodium or potassium salt, that indicates the presence of the respective compound.