How many mole of H2 will be produced if 0.500 grams of magnesium is reacted with 10.00mL of 2.0 M HCl?

I've concluded the answer is 0.02 moles of H2, but I'm doubting myself a lot because I don't understand the aspects of the balanced chemical equation and how that affects the outcome of the answer. Here is my work, please tell me where I've gone wrong in my work, and so forth. Thanks.


2HCl + Mg ---> H2 + MgCl2

.02 mol HCl + .02057 mol Mg --->
0.03mol MgCl2 +0.02mol H2 +0.01057mol Mg

Mg Conversion to moles
0.5g X 1mol Mg/24.305g = 0.02057 mol Mg

HCl Conversion to moles
2.0M HCl = n/0.010L = 0.02moles HCl

Stoichiometry ~
2HCl/1Mg = .02moles HCl/X
X = .01 moles Mg will be consumed

Left Over Mg
.02057 mole Mg - .01 mole Mg = .01057moles Mg after reaction

Moles of MgCl2
.01 moles Mg + .02 moles Cl = .03 moles MgCl2 <-- I think this is wrong and should become .01 moles of MgCl2 because of the 2 on Cl.

moles of H2
Since all 10mL of 2.0M HCl is used up, then .02 moles of H2 is left. <-- I feel this is wrong because of the 2 of Hydrogen, so it should be .01 moles, not .02

Please help me in my confusion

  1. 👍
  2. 👎
  3. 👁
  4. ℹ️
  5. 🚩
  1. This is a limiting reagent problem; we know that because amounts are given for BOTH reactants.
    Mg + 2HCl ==> MgCl2 + H2
    If we had ONLY Mg and all of the HCl needed, then 0.02057 moles Mg x (1 mole H2/1 mole mg) = 0.02057 moles H2 formed.

    If we had 0.02 moles HCl and all the Mg needed, then 0.02 moles HCl x (1 mole H2/2 moles HCl) = 0.02 x 1/2 = 0.01 moles H2 formed.

    Both answers can't be right; the correct answer in limiting reagent problems is ALWAYS the smaller value and the reagent producing that value is the limiting reagent. Therefore, Mg is in excess and all of the HCl is consumed.


    1. 👍
    2. 👎
    3. ℹ️
    4. 🚩
  2. Dr,
    I have another question, but first, thank you for showing me that I was on the right track. I didn't understand how the moles of HCl were distributed. I thought .02 moles of HCl meant that there were .02 moles of H and .02 moles of Cl. Now I know that HCl add up to .02 moles.

    My second question is, how would you find the volume of H2 gas at 1.0atm and 22°C? I've never learned this in class, but must find it for lab. Could you send me in the right direction, or perhaps give me a formula to follow?

    1. 👍
    2. 👎
    3. ℹ️
    4. 🚩
  3. Do you know n = number of moles. Then use PV = nRT and substitute 1 atm for P, V = ?, n = whatever, R is 0.08206 and T is 22 C converted to kelvin.

    OR you may be measuring the volume of gas evolved from a reaction (such as Mg + 2HCl). In that case, you measure volume at room P and T and correct it to standard conditions of 1 atm and 273 K. Usually the gas is collected over water so you use P as room P-vapor pressure H2O at T of the room.

    1. 👍
    2. 👎
    3. ℹ️
    4. 🚩
  4. Thank you Dr. The former is needed to find the volume of H2 in this case. I expect that once I perform the lab, the latter will be needed.
    You've helped me a great deal. You may expect to see me more often. I'm in your care for this semester, amongst any other Chemistry tutors.

    1. 👍
    2. 👎
    3. ℹ️
    4. 🚩

Respond to this Question

First Name

Your Response

Similar Questions

  1. stoichiometry

    Ammonia gas reacts with oxygen gas according to the following equation: 4NH3 + 5O2----4NO + 6H2O a. How many moles of oxygen gas are needed to react with 23 moles of ammonia? (29 mole) b. How may grams of NO are produced when 25


    what is the theoretical mole ratio- NaCl to NaHCO3 How do you determine the percentage error of an experimental mole ratio It would be easier for us to help you if we had the entire problem instead of just parts of it. However,

  3. Chemistry

    A 0.250-g sample of a magnesium-aluminum alloy dissolves completely in an excess of HCl (aq) . When the liberated H2 (g) is collected over water at 29 degrees celsius and 752 torr, the volume is found to be 301 mL . The vapor


    Please explain the answer. Which statement about this reaction is correct? 2Fe(s)+3CO2(g)--->Fe2O3(s)+3CO(g) delta H = 26.6 kJ A. 26.6 kJ of energy are released for every mole of Fe reacted B. 26.6 kJ of energy are absorbed for

  1. Chemistry - Please Check!

    Determine the mass of zinc sulphide, ZnS, produced when 6.2g of zinc and 4.5g of sulphur are reacted. Equation given: Zn + S8 >> ZnS Balanced equation: 8Zn + S8 >> 8ZnS nZn= 6.2 g/ (65.39 g/mol) = 0.095 mol nS8= 4.5 g/(256.48

  2. chemistry

    how many grams of CO2 are produced when 88 grams of O2 are reacted with an excess of butane?

  3. CHEM MOLES !@@!

    Mole Calculation Worksheet 1) How many moles are in 15 grams of lithium? 2) How many grams are in 2.4 moles of sulfur? 3) How many moles are in 22 grams of argon? 4) How many grams are in 88.1 moles of magnesium? 5) How many moles

  4. chemistry

    When magnesium is heated in air, it reacts with oxygen to form magnesium oxide. 2Mg + O2 --> 2MgO If the mass of the magnesium increases by 0.335 g, how many grams of magnesium reacted? A. 0.882 B. 0.441 C. 0.509 D. 1.02 E. Not

  1. Chemistry

    How many grams of MgCl2 are produced when 650 mL of 3 M hydrochloric acid solution reacted with excess magnesium hydroxide solution, Mg(OH)2?

  2. Chemistry

    Upon decomposition, one sample of magnesium fluoride produced 1.65kg of magnesium and 2.58kg of fluorine. A second sample produced 1.38kg of magnesium. How much fluorine (in grams) did the second sample produce?

  3. chemistry

    If 0.81 grams of magnesium oxide are formed, how many grams of oxygen reacted

  4. Chemistry - Stoichiometry

    16.2g of magnesium reacts exactly with 25.3g of fluorine to produce magnesium fluoride, the only product. How many grams of magnesium fluoride could be produced from the reaction of 10.5g of magnesium with excess fluorine. This is

View more similar questions or ask a new question.