Biology; Chemistry; Physics: Post your doubts here!

[Gohar Awais]

This MCQ.

What does a negative gradient of a velocity-time graph indicate,

A. Velocity is increasing.
B. Velocity is decreasing
C. Velocity is constant
D. It does not show velocity at all.


I can't find the answer to it anywhere and my answer is D since the gradient(positive or negative) shows acceleration.

 

[AbeehaH]

Can someone please help me with this?
The volume ratio is 2:1 according to the equation but according to the given it is 1.14 something
So which volume ratio do we use???

 

[AbeehaH]

This MCQ.

What does a negative gradient of a velocity-time graph indicate,

A. Velocity is increasing.
B. Velocity is decreasing
C. Velocity is constant
D. It does not show velocity at all.


I can't find the answer to it anywhere and my answer is D since the gradient(positive or negative) shows acceleration.

I can't find the answer to it anywhere and my answer is D since the gradient(positive or negative) shows acceleration.[/QUOTE]
The answer is B because the gradient is decreasing meaning that the velocity on the y axis is decreasing if the acceleration is negative it is decreasing right? So obviously velocity is decreasing too
It is aa velocity-time graph so it can't be D
If velocity was to be constant then the slope would be 0(no acceleration )

 

[Gohar Awais]

Thanks for the answer I thought it was B. And whatever the molar or volume ratio is given in the equation you use it. Never use the given mass/moles/volumes of the reactants. The given data is used to find limiting reactant.

 

[Mr.Physics]

Can someone please help me with this?
The volume ratio is 2:1 according to the equation but according to the given it is 1.14 something
So which volume ratio do we use???

AbeehaH

 

[AbeehaH]

What is the relationship between density, melting point and boiling point to in terms of the definitions
Someone explain this asap

 

[AbeehaH]

AbeehaH

Why is Mv/n equal for h2so4 and NH3
I am sorry if this is a really dumb question but I suck at this stuff
Thanks a lot though

 

[AbeehaH]

AbeehaH

Why is mv/n equAl
And why dont we use the volumr ratios or limited reagents

 

[Mr.Physics]

Why is Mv/n equal for h2so4 and NH3
I am sorry if this is a really dumb question but I suck at this stuff
Thanks a lot though

Why is mv/n equAl
And why dont we use the volumr ratios or limited reagents

I don't know what are you talking about ?
well I just used the formula, plugged in the values and got the answer. That's it

 

[AbeehaH]

I don't know what are you talking about ?
well I just used the formula, plugged in the values and got the answer. That's it

Where did that formula come from
Is it b3cause of titration?
If we write the balanced equation we can make the volume ratios or something that iswhat i am talking about

 

[AbeehaH]

What is the relationship between density, melting point and boiling point to in terms of the definitions
Someone explain this asap
Why does the density increase down group1 and melting and boiling point decrease down the group?boiling point is proportional to heaviness right? Which is mass.
THE SIZE OF THE ATOM INCREASES DOWN THE GROUP. SO THE MASS INCREASES TOO
Density is directly proportional to mass
So density should be proportional to boiling and melting point.
But the periodic table trends are opposite...... please explain


And is there a relation between melting and boiling point of the same substance


Why is the melting and freezing point of water same is it same for all other substances?


And how do we know if a substance will sunlime without doing any experiments? I mean is there a way to judge this in the exam?



Please answer these four questions ASaP
Thankyou

 

[Metanoia]

Can someone please help me with this?
The volume ratio is 2:1 according to the equation but according to the given it is 1.14 something
So which volume ratio do we use???

Its is not the volume ratio that is 2:1, it is the mole ratio that is 2:1.

moles of H2SO4 = 0.0219 x 0.11 = 0.002409 mol
moles of NH3 = 0.002409 x 2 = 0.004818 mol
mass of NH3 = 0.004818 x 17 = 0.0081906 g
conc of NH3 = 0.0081906/0.025 = 3.27624 g/dm^3

 

[Metanoia]

What is the relationship between density, melting point and boiling point to in terms of the definitions
Someone explain this asap

In simplest terms,

Density : amount of mass per volume e.g. g/cm^3

melting point: temperature at which a substance changes from solid to liquid state

boiling point: temperature at which a substance changes from liquid to gaseous state

Why does the density increase down group1 and melting and boiling point decrease down the group?boiling point is proportional to heaviness right? Which is mass.
THE SIZE OF THE ATOM INCREASES DOWN THE GROUP. SO THE MASS INCREASES TOO
Density is directly proportional to mass
So density should be proportional to boiling and melting point.
But the periodic table trends are opposite...... please explain

Density and melting points/boiling points do not have such a direct correlation as you think.

For metals, the melting and boiling point depends on the metallic bonds, which is partly determined by the amount of electrons in "the sea of elections".

For group I, each ion donates only one electron to the "sea of electrons", this "sea of electrons" gets more "diffused" as ions get larger, so its binding force in keeping the ions together gets weaker.

read the following for more info
http://www.chemguide.co.uk/inorganic/group1/properties.html

And is there a relation between melting and boiling point of the same substance

No direct relation. If you have one, you cannot predict the other based on calculation.

Why is the melting and freezing point of water same is it same for all other substances?

Melting is changing from solid to liquid, freezing is changing from liquid to solid. They should be the same value for a pure substance.

And how do we know if a substance will sunlime without doing any experiments? I mean is there a way to judge this in the exam?

No way to know without testing.

Bonus note: Sublimation (just like melting and boiling) is also dependent on pressure, the temperature involved can change when carried out at different pressure.

 

[AbeehaH]

Now one more question
Pbo+H2--> no réaction because of reactivity series but if we apply heat three is a reaction why is that?
K2O+H2-->no réaction t if we apply heat there is no reaction why is that?
Also in ZnO+H2-->no if we apply heat there is no areaction why is that?

Does this have anything to do with activation energy?
We can find these things by experimentsouth if such a question is in the exam then what is there a rule or anything or are there just some exceptions we need to memorize?

 

[AbeehaH]

In simplest terms,

Density : amount of mass per volume e.g. g/cm^3

melting point: temperature at which a substance changes from solid to liquid state

boiling point: temperature at which a substance changes from liquid to gaseous state


Density and melting points/boiling points do not have such a direct correlation as you think.

For metals, the melting and boiling point depends on the metallic bonds, which is partly determined by the amount of electrons in "the sea of elections".

For group I, each ion donates only one electron to the "sea of electrons", this "sea of electrons" gets more "diffused" as ions get larger, so its binding force in keeping the ions together gets weaker.

read the following for more info
http://www.chemguide.co.uk/inorganic/group1/properties.html


No direct relation. If you have one, you cannot predict the other based on calculation.



Melting is changing from solid to liquid, freezing is changing from liquid to solid. They should be the same value for a pure substance.


No way to know without testing.

Bonus note: Sublimation (just like melting and boiling) is also dependent on pressure, the temperature involved can change when carried out at different pressure.

Thanks a lot man

 

[AbeehaH]

Melting is changing from solid to liquid, freezing is changing from liquid to solid. They should be the same value for a pure substance

Why should they be the same? ??..

 

[bogus]

Melting is changing from solid to liquid, freezing is changing from liquid to solid. They should be the same value for a pure substance

Why should they be the same? ??..

Hi! I'm new here.
Anyway, this is the fixed temperature at which latent heat is used or given out so that particles can adjust their bond formation accordingly.

 

[bogus]

Can someone please explain this question to me? It is from S08

 

[Dashing Cancerian]

Can someone please explain this question to me? It is from S08
View attachment 58755

The gas that will be liberated will be H2 in each case. So the substance Q should be the salt of a metal which is below H in the reactivity series so that H can reduce it. And it would be Cu. For the metal P reaction to occur between it and dilute sulfuric acid it should be a reactive metal thus Zinc should be the choice.
The answer will therefore be D.

 

[bogus]

The gas that will be liberated will be H2 in each case. So the substance Q should be the salt of a metal which is below H in the reactivity series so that H can reduce it. And it would be Cu. For the metal P reaction to occur between it and dilute sulfuric acid it should be a reactive metal thus Zinc should be the choice.
The answer will therefore be D.

Thanks a lot! That makes sense :')