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3 years ago

A 78.0 g sample of an unknown compound contains 12.4 g of hydrogen. what is the percent by mass of hydrogen in the compound?

Chemistry

2 answers:

Harman [31]3 years ago

7 0

Answer:

The percentage by mass of hydrogen in the unknown compound is 15.9 %

Explanation:

The formula to be used here is

% by mass of an element in a compound =

(molar mass of the element ÷ molar mass of the compound) × 100

From the question, the mass of the element (Hydrogen) is 12.4 g

The mass of the compound (unknown) is 78.0 g

Hence,

% by mass of hydrogen in the unknown compound = (12.4 ÷ 78) × 100

= 15.9 %

AleksandrR [38]3 years ago

5 0

Formula to find the percent composition of an element in a compound is $\frac {MolarMassOfElement}{MolarMassOfCompound}*100$ .

Now enter the variables into the formula.

$\frac {12.4}{78.0}*100 = 15.897$ %
Round to 3 significant figures. 15.897% = 15.9%

The answer is 15.9% H

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How much lead(II) chromate (PbCrO4) is precipitated by mixing 100 mL of aqueous 3 M

ICE Princess25 [194]

Answer:

38.8 g of PbCrO₄ are precipitated from the reaction

Explanation:

We have the following chemical reaction:

K₂CrO₄ (aq) + Pb(NO₃)₂ (aq) → 2 KNO₃ (aq) + PbCrO₄ (s)

where:

(aq) - aqueous

(s) - solid

Now we use the following formula to calculate the number of moles:

molar concentration = number of moles / volume (L)

number of moles = molar concentration × volume (L)

number of moles of K₂CrO₄ = 3 × 0.1 = 0.3 moles

number of moles of Pb(NO₃)₂ = 2 × 0.1 = 0.2 moles

We see from the chemical reaction that 1 mole of K₂CrO₄ will react with 1 mole of Pb(NO₃)₂ so 0.3 moles of K₂CrO₄ will react with 0.3 moles of Pb(NO₃)₂ but we have only 0.2 moles of Pb(NO₃)₂ available, so the limiting reactant is Pb(NO₃)₂. Taking this in account we devise the following reasoning:

if 1 moles of Pb(NO₃)₂ produces 1 mole of PbCrO₄

then 0.2 moles of Pb(NO₃)₂ produces X moles of PbCrO₄

X = 0.2 moles of PbCrO₄

number of moles = mass / molar weight

mass = number of moles × molar weight

mass of PbCrO₄ = 0.2 × 194 = 38.8 g

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molar concentration

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3 years ago

The tendency of molecules to move toward areas of lower concentration is called _____.

satela [25.4K]

The correct answer is B. The tendency of molecules to move toward areas of lower concentration is called diffusion. This happens when there is a concentration gradient. This is described by the Fick's laws of diffusion. Diffusion is the net movement of molecules from a higher concentration to lower concentration to achieve equilibrium.

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Question 7

Svet_ta [14]

Answer:

Check if the ions of two compounds exchange places.

Explanation:

The definition of single replacement is a reaction when an ion replaces another ion, thus the name.

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Liquid sodium is being considered as an engine coolant. How many grams of liquid sodium (minimum) are needed to absorb 1.30 MJ o

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Answer:

97 000 g Na

Explanation:

The absortion (or liberation) of energy in form of heat is expressed by:

q=m*Cp*ΔT

The information we have:

q=1.30MJ= 1.30*10^6 J

ΔT = 10.0°C = 10.0 K (ΔT is the same in °C than in K)

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If you notice, the Cp in the question is in relation with mol of Na. Before using the q equation, we can find the Cp in relation to the grams of Na.

To do so, we use the molar mass of Na= 22.99g/mol

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