Lower Secondary Science

[Techmummy]

Can anyone help me with q 27

Thanks in Advance

[S_Mummy]

Please help. Why is b. incorrect.


Which of the following substances is made up of four elements?
a.\t C5H7COOC2H5
b.\tNH4NO3
c.\tK2Cr2O7
d.\tNaHCO3

[Dr.033430Daniel]

Wimpy Kid:

Please help. Why is b. incorrect.


Which of the following substances is made up of four elements?
a.\t C5H7COOC2H5
b.\tNH4NO3
c.\tK2Cr2O7
d.\tNaHCO3

For choice b There is Nitrogen, 4 Hydrogens, then Nitrogen again, then 3 Oxygens. Since Nitrogen is repeated it only counts as one element.

By the way an element symbol always has either one capital letter or a capital and a lower case letter. So an element will never have two capital letters in it's symbol. Sometimes chemists do write chemical formulas where an element is repeated more than once.

Choice d has Sodium, Hydrogen, Carbon and Oxygen - 4 elements.

[S_Mummy]

Hi Dr Daniel & 45has,

Thank you very much for your reply. Ds clearly understands now.

:thankyou:

[anneshirleygilbert]

How do you balance this equation, please.


__Cu + __ HNO3 == __ CU (NO3)2 + __ NO2 + __ H2O

I’ve tried several times but can’t get it.

TIA

[Sysy]

Explain why the walls of atria are thinner than that of the walls of ventricles

Can pls help to explain the qn ?

[The Pasta Greely]

Um hi, do you guys know any good tuitions for Chemistry and Biology for IP (Interragated Programme)? My daughter Rosalinda can’t cope. Any tuition centres besides Joystick? I am already considering Joystick but I still have to think of at least 2 more to compare. Anyone knows?

[Dr.033430Daniel]

Sysy:

Explain why the walls of atria are thinner than that of the walls of ventricles

Can pls help to explain the qn ?

The atria receive blood and then only distribute it a very short distance into the ventricles, so the blood inside the atria is not at a high pressure. The ventricles need to pump the blood to other parts of the body, either the lungs or the rest of the body. So the walls of the ventricles are thick and muscular to provide the pumping action and to withstand the higher pressure.

The right ventricle pumps blood to the lungs. So it has a thinner wall than the left ventricle which has to pump blood to the entire body.

[superkiasume]

anneshirleygilbert:

How do you balance this equation, please.


__Cu + __ HNO3 == __ CU (NO3)2 + __ NO2 + __ H2O

I've tried several times but can't get it.

TIA

According to the guidebook* that I am going through with my son, you should balance chemical equations in this order:
1) Metallic atoms
2) Polyatomic ions
3) Non-metallic atoms other than hydrogen and oxygen
4) Hydrogen and oxygen

So my answer is:
Cu + 4HNO3 --> Cu(NO3)2 + 2NO2 + 2H2O

*Guidebook used: Smashing Exams series.

[concerned_parent1976]

My son is given holiday assignments and the teacher give them this question which he havent learnt ,can some kind soul help me to find the answer for this and the reason why that is the correct answer ?


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