1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
Leokris [45]
3 years ago
13

A certain substance X has a normal freezing point of 5.6 °C and a molal freezing point depression constant Kf-7.78 °C-kg·mol-1.

A solution is prepared by dissolving some urea ((NH2)2CO) in 550. g of Χ. This solution freezes at-0.9 °C. Calculate the mass of urea that was dissolved. Be sure your answer has the correct number of significant digits.
Chemistry
1 answer:
Harrizon [31]3 years ago
7 0

Answer:

27.60 g urea

Explanation:

The <em>freezing-point depression</em> is expressed by the formula:

  • ΔT= Kf * m

In this case,

  • ΔT = 5.6 - (-0.9) = 6.5 °C
  • Kf = 7.78 °C kg·mol⁻¹

m is the molality of the urea solution in X (mol urea/kg of X)

First we<u> calculate the molality</u>:

  • 6.5 °C = 7.78 °C kg·mol⁻¹ * m
  • m = 0.84 m

Now we<u> calculate the moles of ure</u>a that were dissolved:

550 g X ⇒ 550 / 1000 = 0.550 kg X

  • 0.84 m = mol Urea / 0.550 kg X
  • mol Urea = 0.46 mol

Finally we <u>calculate the mass of urea</u>, using its molecular weight:

  • 0.46 mol * 60.06 g/mol = 27.60 g urea

You might be interested in
Which or these equations is balanced H2SO4 + 2Al &gt; Al2(SO4)3 + H2 or 2KCl + Pb(NO3)2 &gt; 2KNO3 + PbCl2
Dmitry_Shevchenko [17]

Balancing of chemical equation is essential because of the law of conservation of mass, which states that the mass of a system can not be created or removed.

The second equation is balanced

2KCl_(_a_q_) +Pb(NO_3)_2_(_a_q_) ==> 2KNO_3_(-a_q_) + PbCl_2(_a_q_)

This is because the number of elements of each atom in the product side equal the number of elements of each atom on the reactant side.

The first equation is not balanced

H_2SO_4 _(_a_q) + 2Al_(_s_) ==> Al(SO_4)_3_(_a_q_) + H_2_(_g_)

This is because there is 1 molecule of SO_4^{-2} on reactant side as compared to 3 molecules of SO_4^{-2}

To balance the equation we add a coefficient of 3 on sulphuric acid (H_2SO_4) and a coefficient of 3 on hydrogen (H_2)

3H_2SO_4_(_a_q_) + 2Al_(_s_) ==> Al(SO_4)_3_(_a_q_) + 3H_2_(_g_)

7 0
3 years ago
A chemist makes 940. mL of sodium carbonate (Na_2CO_3) working solution by adding distilled water to 200. mL of a 0.171 m stock
Alexxandr [17]

Answer:

The answer is 0.0698 M

Explanation:

The concentration was prepared by a serial dilution method.

The formula for the preparation I M1V1 = M2V2

M1= the concentration of the stock solution = 0.171 M

V1= volume of the stock solution taken = 200 mL

M2 = the concentration produced

V2 = the volume of the solution produced = 940 mL

Substitute these values in the formula

0.171 × 200 = 490 × M2

34.2 = 490 × M2

Make M2 the subject of the formula

M2 = 34.2/490

M2 = 0.069795

M2 = 0.0698 M ( 3 s.f)

The concentration of the Chemist's working solution to 3 significant figures is 0.0698M

6 0
3 years ago
What is the oxidation number for Al in Al₂O₃?
sesenic [268]
Oxygen in oxides has oxidation number -2.

<span>Al⁺³₂O⁻²₃

+3*2 -2*3=0</span>
4 0
3 years ago
Element “yellowium” has three naturally occurring isotopes. Below are the masses and relative abundance of each isotope. Find th
katrin [286]
To find average atomic mass, multiply each isotope's atomic mass with its relative abundance and add it all up.

15.012*0.1423 + 16.988*0.3348 + 19.177*0.5229 = 17.851 (5 s.f.)
3 0
3 years ago
_Na3PO4 + __KOH →<br> _NaOH + ___K3PO4
KATRIN_1 [288]
Jdndjdnndndndjxjjxnxnxnxjjxjxjdjdjdjdjdjjdjdhdudhshdhdhhdhdhdhhfhffh
8 0
3 years ago
Read 2 more answers
Other questions:
  • Magnesium and oxygen are likely to form a covalent bond between them. True or false??
    10·1 answer
  • Which reaction is more likely to involve a form of combustion (exothermic)? Explain your reasoning.
    13·2 answers
  • How many grams of H2 are needed to react with 47 grams of N2 to produce 200 grams of NH3?
    9·1 answer
  • Why do gases diffuse more quickly than liquids?
    13·1 answer
  • How do CFC’s illustrate that technical advances can be a “double-edged” sword?
    7·1 answer
  • The simplest method to convert an alcohol to an alkyl halide is by reacting the alcohol with concentrated HCl, HBr, or HI. Compl
    5·1 answer
  • What feature forms on the ocean floor at a divergent plate boundary where two pieces of oceanic crust are moving away from each
    14·1 answer
  • Oil is more dense than water. How will this affect the weight of objects that will float on it?
    9·1 answer
  • How to find nuetrons
    12·1 answer
  • Which compound when dissolved in water, will have the lowest freezing point?
    9·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!