Praxis Practice Test

Question 1

Which of the following will result in a solution of 0.50M HCl?

A. 250mL of 2.0M HCl added to 750mL H2O
B. 500 mL of 1 M HCl added to 1000mL H2O
C. 100mL of 0.50M HCl added to 900mL H2O
D. 200mL of 0.10M HCl added to 1000mL H2O

Answer 1

A. The concentration of the solution that results from adding 250mL of 2.0M HCl to 750mL of water is 0.50M.

Question 2

Johannes Kepler’s greatest contribution to science was that he…

Answer 2

Described the orbits of the planets as ellipses.

Question 3

One similarity between the Bohr and quantum mechanical models of the atom is that electrons…

Answer 3

Are only in certain allowed energy states.

Question 4

When a log burns in a fireplace, producing ash and smoke, which of the following is true?

Answer 4

Energy and matter are both conserved.

Law of conservation of matter, total mass of products=total mass of reactants.

Question 5

The change in Gibbs energy for a reaction at constant temperature is given by the equation deltaG=deltaH-TdeltaS. For an endothermic reaction with deltaH=20,000J and deltaS=100J/K, which of the following is true about the reaction?

Answer 5

It is spontaneous at temperatures above 200K only.

At temperatures greater than 200K, TdeltaS is greater than 20000J and delta G is less than 0.

Question 6

If delta G is less than 0, a reaction is…

Answer 6

Spontaenous

Question 7

If delta G is more than 0, a reaction is…

Answer 7

Non-spontaenous

Question 8

If a beaker and a bathtub are each filled with pure boiling water, which of the following indicates the relative temperatures and heat content of the water in each?

Answer 8

TEMP is the same in both. The HEAT CONTENT is greater in the bath tub.

Question 9

Heat content

Answer 9

Depends on the amount of the substance in the sample and the temperature. Since a bathtub holds more water than the beaker holds, and the temp is same in both, the sample of boiling water in the bathtub has greater heat content than the sample in the beaker.

Question 10

24 11 Na–> X + 0 -1 Beta
Which of the following is formed when a beta particle is emitted from sodium-24, as shown above?

24 12Mg
23 11Na
24 10Ne
20 9F

Answer 10

24 12Mg.

Beta emission process.

Question 11

When a substance undergoes a phase change from a gas to liquid at its boiling point, which of the following properties of the substance always decreases?

Density
Mass
Temperature
Entropy

Answer 11

ENTROPY: it always decreases when a substance undergoes a phase change from a gas to a liquid. Mass and temp are unchanged, and density generally increases with a few exceptions.

Question 12

A sample of liquid water of a certain mass at 20degrees C and 1 atm has a volume of 1,000mL. Which of the following is the most likely volume of a water sample with the same mass at 80 degrees C and 1 atm?

970mL
1000mL
1027mL
4000mL

Answer 12

1027mL.

Volume of a liquid water generally increases in very small increments with increasing temperatures.

Question 13

For which of the following positive changes, separated by the distances shown, will the electrostatic force of repulsion be smallest.

2q (2.00m) 1q
1q (1.00m) 2q
2q (2.00m) 2q
2q (3.00m) 3q

Answer 13

2q (2.00m) 1q

According to Coulomb’s law, the electrostatic force F between two charges q1 and q2 is directly proportional to the product of the charges and inversely proportional to the square of the distance r between the charges.

F=k(q1q2/r^2)

Question 14

True statements about simple machines include which THREE of the following?

A. A simple machine makes the work required to perform a task easier.
B. A simple machine reduces the total amount of work required to perform a task.
C. A simple machine can change the magnitude or direction of a change.
D. The mechanical advantage of a simple machine is the amount by which the machine multiplies the input force.

Answer 14

A, C, D.

Question 15

How would the electromagnetic radiation types be listed in order of increasing energy?

Ultraviolet
Visible
Infrared
Gamma rays

Answer 15

Infrared < visible < ultraviolet < gamma rays

Question 16

A ball is thrown in a horizontal direction. The ball is released at a vertical height of 6ft and with an initial speed along the horizontal direction only, as shown in figure 1. At the same time, an identical ball is dropped from rest from a vertical height of 6 feet, as shown in figure 2. What describes what happens? (Assume that air friction is negligible)

Answer 16

Both balls will hit the ground at the same time.

Due to same gravitational acceleration.

Question 17

If a wire carries a steady current of 0.1amp for 20 seconds, which of the following gives the total charge through the wire during this time interval?

0.005 coulomb
2 coulombs
20 coulombs
200 coulombs

Answer 17

2 coulombs

Electric current is defined as the charge per unit time passing a given point. A current of 1 ampere is equal to 1 coulomb per second. Thus a steady current of 0.1 ampere in 20 seconds corresponds to a total charge of 2 coulombs.

Question 18

A 10kg cart is rolling along the surface shown in the figure above. What is the minimum kinetic energy of the cart at the base of the hill if it is going to be able to roll to the top of the upper level? (Assume g=10m/s2)

4 joules
10 joules
40 joules
400 joules

Answer 18

40 joules

By energy conservation, the sum of the cart’s kinetic energy and potential energy is a constant.

Moving up the hill, kinetic energy will decrease and its potential energy will increase. If cart rests at the top of the hill, it will have only potential energy. Its initial kinetic energy at the top of the hill will have been entirely converted to potential energy.

Thus the minimum kinetic energy of the cart is equal to 10kgx10m/s2x4.0m=400joules

Question 19

The distance between the adjacent nodes of a one-dimensional standing wave is 0.500m. If the frequency of the wave is 100.0Hz, then the speed of the wave is

25m/s
50m/s
100m/s
200m/s

Answer 19

100m/s

v=fwavelength
v=100Hz1m=100m/s

Question 20

Two astronauts, of masses 60kg and 80kg, are initially at rest in outer space. They push each other apart. If the speed of the lighter astronaut is 12m/s, what is the speed of the heavier astronaut?

4m/s
9m/s
12m/s
16m/s

Answer 20

9m/s

m1v1=m2v2 gives:

v1=(60kg*12m/s)/80kg=9m/s

Question 21

The device has an input voltage of 25V and an output voltage of 50V. The device has a soft iron core, a primary coil of 5 turns and a secondary coil of 10 turns. It is a…

resistor
capacitor
battery
transformer

Answer 21

Transformer–a device which inductively couples two AC circuits and can be used to step up voltage or step down voltage.

Question 22

If a flat object is placed 3 meters in front of a plane mirror, the image will be formed…

A. On the surface of the mirror
B. 3 meters behind the surface of the mirror
C. Greater than 3 meters behind the surface of the mirror
D. Less than 3 meters behind the surface of the mirror.

Answer 22

B. For a plane mirror, the image distance is equal to the object distance.

Question 23

A tractor is pulling a wagon full of hay. The mass of the wagon and hay is two times the mass of the tractor. When the tractor accelerates forward, the force that the wagon exerts on the tractor is…

Answer 23

Equal in magnitude to the force that the tractor exerts on the wagon.

Newton’s third law states that for every action, the reaction force is equal in magnitude but opposite in direction to the action force. Thus the force that the wagon exerts on the tractor must be equal in magnitude to the force that the tractor exerts on the wagon.