Unit 6 . 1-5 (exam 3)

Pressure

force over area

weight of something on an object

P = force/area

1 atmosphere (atm)

1 atmosphere (atm) = 760 mmHg or 760 torr.

atmosphere (atm) - room air pressure

Category 5 hurricanes often have a central air pressure of 690.1 torr. convert this pressure to atmosphere

1 atmo = 760 torr

690.1 torr x 1 atmo/760 torr = 0.908 atm

suppose blood pressure readings were reported in cm Hg rather than mmHg. convert 140/90 mmHg to cm Hg. (1 in = 2.54cm)

l cm = 10 mm

10^-2 10^-3 = 10¹ =10

140 mmHg x 1 cm Hg/10 mmHg = 14 cm Hg

90 mmHg x 1 cm Hg/10 mmHg = 9cm Hg

four measurable quantities of a gas

1. pressure (p): atm

2. volume (V) liters

3. Temperature (T): kelvin (absolute temp scale) no negative kelvin values

4. amount in moles (n): mol

Boyle’s law

P₁V₁ = P₂V₂

Pa 1/v (Boyle’s law is breathing)

a = alpha means proportional

pressure and volume

• pressure goes up, volume goes down

• pressure goes down, volume goes up

Charles’s law

V₁/ T₁ = V₂/T₂

_V ∝ _T

volume and temperature

• volume increases with increasing temp

• volume decrease with decreasing temp

sea breeze is created by charles’s law

Guy-Lussac’s law

P₁/T₁ = P₂/T₂

pressure and temperature

• pressure increases with increasing temp.

• pressure decreases with decreasing temp.

P ∝T

proportional

P ∝ V - inversely proportional

P ∝ 1/v - only 1/variable

V ∝ T

V ∝ N

P ∝ T

Directly proportional increase so does the other (increase)

decrease so does the other decrease

Combined gas law

P₁V₁/T₁ = P₂V₂/T₂

_{1: state 1 (change) → state 2 (predicts what is 2)}

_{ex. change the temp (T), pressure (P), volume (V)}

_{if a problem provides:}

_{p and V:}

_{P1V1 = P2V2}

_{P and T:}

_{P1/T1 = P2/T2}

_{V and T:}

_{V1/T1 = V2/T2}

Avogadro’s Law

Volume increase with increasing amount of gas (moles)

V1/ n1 = V2/n2

V∝N

A 4.0-L container of helium gas has a pressure of 10.0 atm, what pressure does the gas exert if the volume is increased to 6.0 L?

1. ID the variables and derive the gas law

   P1V1 =P2V2

2. match variables

V1= 4.0 L

P1 = 10.0 atm

V2 6.0 L

P2 =?

P2 = P1V1/V2 = 10.0 atm (4.0L)/6.0 L = 40.0/6 = 6.67 atm = 6.7

P ∝ 1/v - v went up and P went down

What volume will a sample of gas occupy at 400 °C, if it occupies 420 mL at 100 °C at constant pressure?

T go up and V go up

K = C + 273

V1 = 420 mL

V1/T1 = V2/T2

420 mL/373 k = v2/673 k

673 × 1.126 =v2/673 × (673) (you times to cancel out the divided) = 758 mL

volume is higher

Argon is an inert gas used in incandescent light bulbs to slow the vaporization of the filament.  A certain light bulb containing argon at 1.20 atm and 18 °C is heated to 85 °C at constant volume.  What is the final pressure of argon in the bulb in atm?

P1 = 1.20 atm

k = c +273

p1/T1= P2/T2

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another way to solve it

P1/T1= P2/T2 (do the criss-cross method)

P1T2 = P2T1

1.20 atm (358k) = p2 (291K)

P2 = 1.20 atm (358K)/ 291 K = 1.48 atm

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3 H₂(g) + N₂(g) → 2NH₃(g)

How many liters of NH₃ would be produced when 2.9 L of H₂ reacts with an excess of N₂ at constant temperature and pressure?

Avogadro’s law - stoichiometry ( sub volume in liters for the molar coefficient)

V1/n1 = V2/n2

1. start with the correct ratio

2NH₃ liters / 3H₂ liters x 2.9 L of H2 = 1.9 L of NH3

solute

in the minority/smallest component in a solution (mixture)

solvent

is the majority largest component in a solution

solution

homogenous mixture, uniform throughout. (all mix well - you cannot see)

small particles size, transparent/translucent - see through

ex. apple juice

colloid

homogenous mixtures, uniform throughout,

large particles size, opaque (cant see through)

the middle largest component

suspension

heterogenous mixtures, non-uniform ( you can see the mixtures)

largest particles. undisturbed, the particles settle to the bottom.

Ex. blood ( it is consitly moving in are body. if not it will clot)

pulp orange juice

weight to volume (w/v)%

g solute/ mL solution x 100

volume to volume (V/V)

volume of solute/ volume of solution x 100

parts per million (ppm)

if you see a chemical given in ppm, its dangerous

ppm= same unit to be (g, mg, mL…) solute / share unit (g, mg, mL…) solvent x 10⁶ → 1,000

Seabirds such as osprey that feed on fish contaminated with the pesticide DDT (sample Problem 7.7) accumulate an average of 25 parts per million of DDT in their fatty tissues. when DDT concentration is high, mother osprey produces eggs with very thin shells that are easily crushed, so fewer osprey chick’s hatch.

25 mg DDT/ 1,000,000 mg mixture x 10⁶ = 25 ppm

Molarity (M)

molarity in lab reports .

(Moles/L sometimes)

chemists density → M moles/Liters

use those 2 triangles for calculations

Dilution

high concentration add solvent, make a lower concentration solution.

M1V1 = M2V2

M = molarity (for concentrations)

M can also mean mega

V = volume

Calculate the concentration of a solution and prepare a dilute solution - Practice

A saline solution used in intravenous drips contain 0.92% (w/v) NaCl in water.  How many grams of NaCl are contained in 250 mL of this solution

G?

0.92 g NaCl/100mL solution x 250/1 mL solution = 2.3 g NaCl

Calculate the concentration of a solution and prepare a dilute solution - Practice

What is the concentration in parts per million (ppm) if 0.038 mg of DDT was found in 1400 g plankton?

1. convert to the same units

0.038 mg → g or 1400 g to mg

100g x 1 mg/10^-3 g = 1,400,00 mg (1.4 × 10⁶ mg)

2. apply formula

0.038 mg DDT/ 1.4 × 10⁶ mg (10⁶) the two cancel out

and you divide by 0.038 mg DDT/ 1.4 = 0.027 ppm

Calculate the concentration of a solution and prepare a dilute solution - Practice

Calculate the molarity of a solution made from 20.0 g of NaOH in 250 mL of solution.

Molar mass of NaOh is 40.0 g/mol

M?

M=moles/L

moles/L: 1 mole/40.0g x 20.0 g NaOH/2.50 mL x 1000 mL/ 1 L = 2.0 mole/L = 2.0 M

or solve

250 mL/ 1000 mL

20 g/40 g/mol = 0.5 moles

0.5 moles/0.250 L = 2.0 M

Calculate the concentration of a solution and prepare a dilute solution - Practice

What volume in milliliters of a 0.30 M solution of glucose contains 0.025 mol of glucose?

any molarity (M) = moles/L

0.30 M = 0.30 moles/1 L

mL?

1000 mL/ 1L x 1L/0.30 moles x 0.0250 mol/ 1 = 83.3 mL

or

L = mol/M

0.025 moles/0.30 M

= 0.0833 L (1000 mL/1)

= 83.3 mL

Calculate the concentration of a solution and prepare a dilute solution - Practice.

What is the concentration of a solution formed  by diluting 5.0 mL of 3.2 M glucose solution to 40.0 mL?

v1 = 5.0 mL

M1 = 3.2 M

v2= 40.0 mL

M2?

M1V1/V2 = M2V2/V2 (the two V2 cancel out)

M2 = M1V1/V2 = 3.2 M (5.0 mL)/ 40.0 mL

= 0.4 M solution

a 25% (wt/vol) solution of mannitol is often used to help patients with head injuries to reduce swelling. What volume, in mL, should be give to a patient requiring 57g?

mL?

100mL/25g x 57g/1 = 228mL