Learn Hardcore Swahili: Kesho tutatumia kipima joto darasani kufanya jaribio. - Tomorrow we will use a thermometer in class to do an experiment.

The infinitive kufanya means to do and here it expresses purpose: use a thermometer … to do an experiment. You can add ili to make the purpose explicit, but it isn’t required.

Without ili (very common): … tutatumia … kufanya jaribio.
With ili (more explicit): … tutatumia … ili kufanya jaribio.

What exactly does darasani mean, and is it the same as katika darasa?

Darasani is the locative form of darasa (class/classroom) and means in class or in the classroom. It’s made by adding the locative suffix -ni.

darasani = in class/in the classroom (most idiomatic)
katika darasa = in the classroom (also correct) Avoid doubling the locative: don’t say katika darasani.

Should kipima joto be written as one word or two? What’s the plural?

Both kipima joto and kipimajoto are seen. Many dictionaries prefer the fused form kipimajoto. It’s a Ki-/Vi- class instrument noun (thing for measuring heat).

Singular: kipimajoto (or kipima joto)
Plural: vipimajoto (or vipima joto)

Where can Kesho go, and does moving it change the meaning?

Time words are flexible. Meaning stays the same; you just shift emphasis.

Kesho tutatumia kipima joto darasani kufanya jaribio. (neutral)
Tutatumia kipima joto darasani kufanya jaribio kesho.
Darasani kesho tutatumia kipima joto kufanya jaribio. (emphasizes the place/time you put up front)

Can I include an object marker for kipima joto?

Yes, if the thermometer has already been mentioned. For Ki-/Vi- nouns, the object marker is ki- (singular) / vi- (plural).

With explicit object (typical): Tutatumia kipima joto.
With object marker only (when it’s already known): Tutakitumia. Avoid doubling (using both OM and full noun) in careful Standard Swahili: Tutakitumia kipima joto is often seen as redundant for inanimate objects.

How do I make the sentence negative?

Use the negative subject prefix plus -ta-:

Kesho hatutatumia kipima joto darasani kufanya jaribio. = Tomorrow we will not use a thermometer in class to do an experiment. Other persons for reference:
I will not use: sitatumia
You (sg) will not use: hutatumia
He/She will not use: hatatumia
We will not use: hatutatumia
You (pl) will not use: hamtatumia
They will not use: hawatatumia

What’s the difference between jaribio and mtihani?

jaribio = an experiment, trial, attempt, test (in the sense of trying something out or a scientific test)
mtihani = an exam/test (assessment at school) So a science experiment is a jaribio, while a math exam is a mtihani.

How do I say “science experiment” or “experiments” in this sentence?

Use jaribio la sayansi (class 5 agreement) and majaribio ya sayansi for the plural.

Singular: … kufanya jaribio la sayansi.
Plural: … kufanya majaribio ya sayansi.

Could I express the idea as “by using a thermometer” instead?

Yes. Use kwa kutumia:

Kesho darasani tutafanya jaribio kwa kutumia kipimajoto. This emphasizes the means (by using) rather than simply stating use.

Is the order of darasani and kufanya jaribio fixed?

No—adverbials are flexible. Both are fine:

… kipima joto darasani kufanya jaribio. (place, then purpose)
… kipima joto kufanya jaribio darasani. (purpose, then place) Choose the order that matches what you want to emphasize or what sounds smoother to you.

Can I use na instead of kwa kutumia to mean “with a thermometer”?

Yes:

Tutafanya jaribio na kipimajoto. = We will do an experiment with a thermometer.
Tutafanya jaribio kwa kutumia kipimajoto. = We will do an experiment by using a thermometer (slightly more explicit about the instrumentality).

How do I change the subject: I/you/they will use?

Swap the subject prefix:

I will use: nitatumia
You (sg) will use: utatumia
He/She will use: atatumia
We will use: tutatumia
You (pl) will use: mtatumia
They will use: watatumia

Any quick pronunciation tips for kipima joto, darasani, and jaribio?

Swahili stress is on the second-to-last syllable.
Syllables: ki-pi-ma jo-to, da-ra-sa-ni, ja-ri-bi-o.
Vowels are pure (no diphthongs), and j is like English j in jam.

Is jaribio related to kujaribu? Can I say tutajaribu here?

Yes, they share the root jarib- (try/test).

kujaribu = to try/attempt.
jaribio = an attempt/test/experiment (the noun).
In this context, kufanya jaribio = to do an experiment. Tutajaribu would mean we will try (something), not we will do an experiment.

Can I add sisi for emphasis on “we”?

Yes. Put it before the verb:

Sisi tutatumia kipima joto darasani kufanya jaribio.
This stresses we (as opposed to someone else).

What if I want to say “at school” rather than “in class”?

Use shuleni (locative of shule = school):

Kesho tutatumia kipima joto shuleni kufanya jaribio.
shuleni = at school; darasani = in the classroom/in class (more specific).