1. write and balance the equation wuth reacyion of metal with hydrocholric acid:
ID: 1005150 • Letter: 1
Question
1. write and balance the equation wuth reacyion of metal with hydrocholric acid: na, al, zn, ca
2. .04250 g of mg is reacted with excess hcl , calculate theoretical volume at stp of hydrogen gas produced
3. 44 ml of h is collected over water from above reaction conducted at 22°c and 759.2 torr, calculate the volume of dey H produced at stp
4. calculate the percentage error of this experiment
5. explain the reason for each of the golling procedures
A. cleaning mg strip with sandpaper
B.equalizing the water levels insude and outside the eudiometer
Explanation / Answer
1
Metals react with acid to give salt and Hydrogen gas.
Metal + Acid = Salt + H2(g)
2Na + 2HCl = 2NaCl + H2(g)
2Al + 6HCl = 2AlCl3 + 3H2
Zn + 2HCl = ZnCl2 + H2
Ca + 2HCl = CaCl2 + H2
2.
0.425 g of Mg reacted with excess HCl.
Mg + 2HCl = MgCl2 + H2
Let us determine the moles of limiting reactant.
Mg = 0.425g/24.3050 = 0.0175 moles of Mg
As per the reaction, 1 mole of Mg with excess HCl produces 1 mole of H2 gas.
Moles of H2 = 0.0175 moles.
At STP 1 mole of gas occupies 22.4 L of volume.
Volume = 0.0175 * 22.4 = 0.392 L of H2
3.
44 ml of H2 collected from above reaction at 22C and 759.2 torr. Let us calculate the volume of H at STP.
This is an example of combined Gas law problem.
P1V1/T1 = P2V2/T2
As H2 was collected over water. Both water and gas contribute to the pressure of the wet gas.
According to the Dalton’s law of Partial pressures.
Pgas + PH2O = Patm
At 22.0°C, the vapour pressure of water is 19.83 torr.
Pgas = Patm – PH2O = 746 – 19.83 = 726.17 torr
T1 is 22 + 273.15 = 295.15 K
Summary:
P1 = 726.17 torr, V1 = 44 ml, T1 = 295.15 K
P2 = 760 torr, V2 = ? , T2 = 273.15 K
P1V1/T1 = P2V2/T2
V2 = V1 * P1/P2 * T2/T1
44 * 726.17/760 * 273.15/295.15 =
The volume of dry H2 is 38.91 ml
4.
Percentage error in above experiment –
= Experimental value – theoretical value/theoretical value * 100
= 44 - 38.91/38.91 * 100 = 13.08 %
5.
A .Mg is alkali metal. It is in the second column from the left on the periodic table. Alkali metals are reactive to oxygen and water. So, when Mg is exposed to air it is coated with Magnesium oxide. This coat makes the ribbon harder to ignite. Also it can increase error in calculations as the weight of actual Mg will be slightly different.
B. Equalizing the level inside and outside ensures that the pressure inside the tube is exactly the same as the atmospheric pressure. If the level of the water outside the tube is higher than inside, then it will be equalized by gravity. That will cause an upward push on the water inside that will compress the gas, raising the pressure, and giving us incorrect (low) volume reading. The converse will be true if the level inside is higher than outside.
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