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2 years ago

A form of energy that is stored in a stretched rubber band is called

1 answer:

6 0

You input potential (stored) energy into the rubber band system when you stretched therubber band back. Because it is an elastic system, this kind of potential energy is specifically called elastic potential energy. ... When the rubber band is released, the potential energy is quickly converted to kinetic (motion) energy.

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An atom has atomic number of 34. how many protons and electrons does it have? what is its symbol? 34 protons and electrons. se l

AURORKA [14]

Se: Selenium

Protons: 34
Electrons: All atoms in the periodic table are neutral until changed otherwise
Neutrons: 44
Atomic Mass: 78.09

>Symbol attached<

4 0

2 years ago

PLEASE HELP! ONLY SERIOUS ANSWERS! I APPRECIATE ANYTHING!! 30PTS!!!

xenn [34]

1 is b 2 is a 3 is d 4 is a 5 is c

5 0

3 years ago

In the titration of HCl with NaOH, the equivalence point is determined

kondaur [170]

Answer:

In the titration of HCl with NaOH, the equivalence point is determined from the point where the phenolphthalein turns pink and then remains pink on swirling.

Explanation:

The equivalence point is the point at which exactly enough titrant (NaOH) has been added to react with all of the analyte (HCl). Up to the equivalence point, the solution will be acidic because excess HCl remains in the flask.

Phenolphtalein is chosen because it changes color in a pH range between 8.3 – 10. Phenolphthalein is naturally colorless but turns pink in alkaline solutions. It remains colorless throughout the range of acidic pH levels, but it begins to turn pink at a pH level of 8.3 and continues to a bright purple in stronger alkalines.

It will appear pink in basic solutions and clear in acidic solutions.

The more NaOH added, the more pink it will be. (Until pH≈ 10)

In strongly basic solutions, phenolphthalein is converted to its In(OH)3− form, and its pink color undergoes a rather slow fading reaction and becomes completely colorless above 13.0 pH

a. from the point where the pink phenolphthalein turns colorless and then remains colorless on swirling.

⇒ the more colorless it turns, the more acid the solution. (More HCl than NaOH)

b. from the point where the phenolphthalein turns pink and then remains pink on swirling.

The equivalence point is the point where phenolphtalein turns pink and remains pink ( Between ph 8.3 and 10). (

Although, when there is hydrogen ions are in excess, the solution remains colorless. This begins slowely after ph= 10 and can be noticed around ph = 12-13

c. from the point where the pink phenolphthalein first turns colorless and then the pink reappears on swirling.

Phenolphthalein is colorless in acid solutions (HCl), and will only turn pink when adding a base like NaOH

d. from the point where the colorless phenolphthalein first turns pink and then disappears on swirling

Phenolphthalein is colorless in acid or neutral solutions. Once adding NaOH, the solution will turn pink. The point where the solution turns pink, and stays pink after swirling is called the equivalence point. When the pink color disappears on swirling, it means it's close to the equivalence point but not yet.

3 0

2 years ago

Karl likes to use cruise control when he drives on

Yanka [14]

Answer:

3.96 MINUTES

Explanation:

Karl likes to use cruise control when he drives on

the highway. After setting cruise control at 33.53

m/s (75 mph). At this speed, how long would it

take Karl to travel 8 kilometers?

VELOCITY = DISTANCE/TIME

V=D/T

VT=D

T=D/V

THE DISTANCE IS 8 KM

THE VELOCITY IS 75 MPH

THERE ARE 1.61 KM PER MILE

75M[H =

75 X 1.61 KM/H =

121 KM/HR

T=D/V

T=8/121 =0.066 HOUR =

0.066 X 60 MINUTES =

3.96 MINUTES

CHECK

75 MPH =

(75 X 1.61) KM/60 MINUTES =

120,75 KM/60 MINUTES=

2.01 KM/MINUTE

to travel 8 K,M WILL TAKE

8/2.01 = 3.98 minutes

3 0

2 years ago

Solid sodium hydrogen carbonate, NaHCO3, decomposes on heating according to the equation:

tekilochka [14]

Answer:

See explanation

Explanation:

First, let's write the balanced equation again:

2 NaHCO3(s) <-> Na2CO3(s) + H2O(g) + CO2(g)

Now, we know that the total pressure was 7.76 atm. This total pressure, is the sum of the pressure of water and CO2 like this:

Ptotal = Pwat + PCO2 (1)

This is the dalton's law for partial pressures.

The pressure can be also be relationed with the moles

Ratio of mole = Ratio of pressure

so, taking this in consideration we can say the following:

Pwater/PCO2 = moles water / moles CO2

As the only components exerting pressure are CO2 and Water (Because they are in gas phase), the total pressure can be splitted between the two of them so:

Pwater = Ptotal/2

Pwater = 7.76 / 2 = 3.88 atm

With this pressure, and using the ideal gas equation, we can know the moles of water:

PV = nRT

n = PV/RT using R = 0.082 L atm / K mol

n = 3.88 * 5 / 0.082 * (160+273)

n = 0.546 moles of water

b) now that we have the moles of water, we can actually know the moles that reacted originally from the sodium carbonate by stechiometry.

2NaHCO3(s) <-> Na2CO3(s) + H2O(g) + CO2(g) MMCO2 = 84 g/mol

the moles of NaHCO3 initially:

n = 100 / 84

n = 1.19 moles

so, If 1.19 moles of NaHCO3 reacted, and only produces 0.546 moles of water and CO2, then, the remaining moles of NaHCO3 is:

remaining moles = 1.19 - 0.546 = 0.644 moles

therefore the mass remaining:

mCO2 = 0.644 * 84

mCO2 = 54.096 g

c) As it was stated before, only the gaseous components are involved in the pressure, thus, in the kp expression which is:

Kp = Pwater * PCO2

Kp = 3.88 * 3.88

Kp = 15.0544

d) As the total pressure is 7.76 atm and the fact that NaHCO3 is solid, this component is not exerting any pressure in the reaction, as seen in the Kp expression, so it won't matter that if we raise a little the quantity of the reactant, it still has some remaining.

3 0

3 years ago