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Stella [2.4K]
3 years ago
9

Even though we are well into the course Dumbledore notices some of the students are still having trouble with significant figure

s. Let’s review them once more: How many significant figures does the result of the following calculation have? (3.478-2.31)*(4.428-3.56)?
A) 1
B) 2
C) 3
D) 4
E) 5 2.
Chemistry
1 answer:
Sphinxa [80]3 years ago
5 0

Answer:

B) 2

Explanation:

Significant figures : The figures in a number which express the value -the magnitude of a quantity to a specific degree of accuracy is known as significant digits.

The rule apply for the multiplication and division is :

The least number of significant figures in any number of the problem determines the number of significant figures in the answer.

The rule apply for the addition and subtraction is :

The least precise number present after the decimal point determines the number of significant figures in the answer.

(3.478-2.31) = 1.168 ≅ 1.17 (Rounded to least decimal digit)

(4.428-3.56) = 0.868 ≅ 0.87 (Rounded to least decimal digit)

So,

1.17 * 0.87 = 1.0  (Rounded to least significant)

Answer - two significant digits

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The vapor above a mixture of pentane and hexane at room temperature contains 35.5% pentane by mass. What is the mass percent com
FrozenT [24]
  • The mass percent of Pentane in solution is 16.49%
  • The mass percent of Hexane in solution is 83.51%

<u>Explanation</u>:

  • Take 1 kg basis for the vapor: 35.5 mass% pentane = 355 g pentane with 645 g hexane.
  • Convert these values to mol% using their molecular weights:

Pentane: Mp = 72.15 g/mol -> 355g/72.15 g/mol = 4.92mol

Hexane: Mh = 86.18 g/mol -> 645g/86.18 g/mol = 7.48mol

Pentane mol%: yp = 4.92/(4.92+7.48) = 39.68%

Hexane mol%: yh = 100 - 39.68 = 60.32%

Pp-vap = 425 torr = 0.555atm

Ph-vap = 151 torr = 0.199atm

  • From Raoult's law we know:  

Pp = xp \times Pp - vap = yp \times Pt                                       (1)

Ph = xh \times Ph - vap = yh \times Pt                                       (2)

  • Since it is a binary mixture we can write xh = (1 - xp) and yh = (1 - yp), therefore (2) becomes:

(1 - xp) \times Ph - vap = (1 - yp) \times Pt                                   (3)

  • Substituting (1) into (3) we get:

(1-xp) \times Ph - vap = (1 - yp) \times xp \times Pp - vap / yp            (4)

  • Rearrange for xp:

xp = Ph - vap / (Pp - vap/yp - Pp - vap + Ph - vap)      (5)

  • Subbing in the values we find:

Pentane mol% in solution: xp = 19.08%  

Hexane mol% in solution: xh = 80.92%

  • Now for converting these mol% to mass%, take 1 mol basis for the solution and multiplying it by molar mass:

mp = 0.1908 mol \times 72.15 g/mol

     = 13.766 g

mh = 0.8092 mol \times 86.18 g/mol

     = 69.737 g

  • Mass% of Pentane solution = 13.766/(13.766+69.737)

                                                       = 16.49%

  • Mass% of Hexane solution  = 83.51%
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Consider the given examples listed here, find out which substance from the list will turn phenolphthalein pink? (a) vinegar ( b)
egoroff_w [7]

Answer:

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Explanation:

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A soap solution is usually basic. Since phenolphthalein turns pink in an alkaline solution, then when phenolphthalein is added to a soap solution, the solution soon turns pink because it is alkaline in nature.

As a matter of fact, a soap sometimes has almost the pH of baking soda!

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At constant pressure and 25^0C , a sample of gas occupies 4.5lit. at what temperature will the gas occupy 9.0lit.​
olga55 [171]

Answer:

Final temperature = 149 K

Explanation:

Given data:

Initial temperature = 25°C (25+273 = 298 K)

Initial volume = 4.5 L

Final temperature = ?

Final volume = 9.0 L

Solution:

The given problem will be solve through the Charles Law.

According to this law, The volume of given amount of a gas is directly proportional to its temperature at constant number of moles and pressure.

Mathematical expression:

V₁/T₁ = V₂/T₂

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T₁ = Initial temperature

V₂ = Final volume  

T₂ = Final temperature

Now we will put the values in formula.

V₁/T₁ = V₂/T₂

T₂ = T₁V₂/V₁  

T₂ = 4.5 L × 298 K / 9.0 L

T₂ = 1341 L K / 9.0L

T₂ = 149 K

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The atoms of different chemical elements can be differentiated based on the number of protons.

Each chemical element is differentiated by his number of protons. This number of protons is also knowing as atomic number and it is represented by the letter (Z).

The atomic number represented the number of protons in the nucleus of an element. For example:

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<h3>What is an atom?</h3>

The atom is the smallest part of the composition of matter, it is indivisible and is composed of a nucleus that has protons and neutrons, and around the nucleus there are the electrons.

Learn more about the atom at: brainly.com/question/17545314

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